Request Fullfilled 

Ok. I think I took care of everything.  I wrote a bunch of tests to catch errors. And then tested a bit.

Binaries for windows 7+ and osx available here:

https://github.com/RobJames-Texas/TL2_ItemDatMaker/releases

I added functionality so that you should be able to drag and drop your mesh file from your mod folder onto the exe and it should then ask you for the rest of the parameters.

Let me know if you have any issues.

Here I'll make a rundown of what the script should do:

Given a 3d model as input, that means the file name and folder location, the scritp should generate a corresponding item unit file in a specific folder.

Example:
Input: D:\Steam\SteamApps\common\Torchlight II\MODS\ITEM_MOD\MEDIA\MODELS\WEAPONS\_SWORDS\Sword_model_01

Unit file:
Created in:  D:\Steam\SteamApps\common\Torchlight II\MODS\ITEM_MOD\MEDIA\UNITS\ITEMS\SWORDS\
[UNIT]
        <STRING>RESOURCEDIRECTORY:media/models/weapons/_Swords
<STRING>MESHFILE:Sword_model_01
[/UNIT]
List of folders equivalencies

Spoiler (hover to show)

_AXES = AXES
_BOWS = BOWS
_CANNONS = CANNONS
_CROSSBOWS = CROSSBOWS
_FISTS = FISTS
_GREATAXES = 2HAXE
_GREATHAMMERS = 2HMACE
_GREATSWORDS = 2HSWORD
_HAMMERS = MACES
_PISTOLS = PISTOLS
_POLEARMS = POLEARMS
_RIFLES = RIFLES
_SHIELDS = SHIELDS
_STAVES = STAVES
_SWORDS = SWORDS
_WANDS = WANDS

Now, this file is totally imcomplete, it needs some basic things, a name, a unittype and a base file. But this things are related to one variable, rarity.

So a second input should be item rarity, the options being, Normal, Magic (Blue), Unique and Legendary. With this we can determine the base file and the unittype of the item. The type of item, that being an sword, axe, greataxe, etc, should be determined using the folder in which the model is stored.

Example:
Rarity input: Magic
Unit file:
[UNIT]
        <STRING>BASEFILE:media\units\items\swords\base_sword_magic.dat
<STRING>UNITTYPE:MAGIC 1HSWORD
[/UNIT]
List of folder name and base file equivalency

Spoiler (hover to show)

_AXES = BASE_AXE
_BOWS = BASE_BOW
_CANNONS = BASE_CANNON
_CROSSBOWS = BASE_CROSSBOW
_FISTS = BASE_FIST
_GREATAXES = BASE_2HAXE
_GREATHAMMERS = BASE_2HMACE
_GREATSWORDS = BASE_2HSWORD
_HAMMERS = BASE_MACE
_PISTOLS = BASE_PISTOL
_POLEARMS = BASE_POLEARM
_RIFLES = BASE_RIFLE
_SHIELDS = BASE_SHIELD
_STAVES = BASE_STAFF
_SWORDS = BASE_SWORD
_WANDS = BASE_WAND

List of folder name and unittype equivalencies

Spoiler (hover to show)

_AXES = 1HAXE
_BOWS = BOW
_CANNONS = CANNON
_CROSSBOWS = CROSSBOW
_FISTS = FIST
_GREATAXES = 2HAXE
_GREATHAMMERS = 2HMACE
_GREATSWORDS = 2HSWORD
_HAMMERS = 1HMACE
_PISTOLS = PISTOL
_POLEARMS = POLEARM
_RIFLES = RIFLE
_SHIELDS = SHIELD
_STAVES = STAFF
_SWORDS = 1HSWORD
_WANDS = WAND

Exception, there is no _legendary base file, they use the unique base file.

Now for the name, the name should follow the vanilla convention with a tag added. the tag should be another input. ([itemtype]_[TAG][Rarityletter][Number])

Example:
Input tag: TEST

Unit file:
[UNIT]
<STRING>NAME:sword_TESTm01
[/UNIT]
Now the last input should be item level, but to make the script have extra option, it should have 2 funtions:
Make Alternative clones, creates two more files using the first as base increasing its level by a predefined amount
Make NG+ Clones, this one should be one of the more interesting function. It would make clones of the item increasing their level simulating the NG+ calculation of GUTS for increasing level.

Example:

Input item level: 15
Make Alt Clones [Y/N]: Y

Unit file:
[UNIT]
<INTEGER>LEVEL:15
<INTEGER>MINLEVEL:13
<INTEGER>MAXLEVEL:19
[/UNIT]
Alternative Clones:
B:
[UNIT]
        <STRING>NAME:sword_TESTm01b
<STRING>BASEFILE:media\units\items\swords\sword_TESTm01.dat
<INTEGER>LEVEL:19
        <INTEGER>MINLEVEL:17
<INTEGER>MAXLEVEL:22
[/UNIT]

C
[UNIT]
        <STRING>NAME:sword_TESTm01C
<STRING>BASEFILE:media\units\items\swords\sword_TESTm01.dat
<INTEGER>LEVEL:23
        <INTEGER>MINLEVEL:21
<INTEGER>MAXLEVEL:26
[/UNIT]

The MINLEVEL should be LEVEL-2, and MAXLEVEL = LEVEL + 3. The increase in level for the alternatives should be LEVEL+4.

Now how should the "Make NG+ Clones" work, the clones should have a level increase using the equation:

For Item level in the NG range (default 0<i-level<=50)

NG+ Clone (default range : 51 to 80)
I-LevelNG+= 51+[(i-level/50) * (80-51)]

NG++ clone (default range : 81 to 100)
I-levelNG+2 = 81+[(i-level/50) * (100-81)]

NG+++ Clone (default range : 101 to 120)
I-levelNG+3 = 105

For item level in the NG+ range (default 51<=i-level<=80)

NG++ clone (default range : 81 to 100)
I-levelNG+2 = 81+{[(i-level-50)/(80-50)] * (100-81)}

NG+++ Clone (default range : 101 to 120)
I-levelNG+3 = 105

For item level in the NG++ range (default 81<=i-level<=100)
NG+++ Clone (default range : 101 to 120)
I-levelNG+3 = 105

This option should be able to interact with "make alternative clones" in a way that every alteranative clone, get their corresponging NG+ clones.

Example:

Input item level: 15
Make Alt Clones [Y/N]: N
Make NG+ Clones [Y/N]: Y

Unit file:
[UNIT]
<INTEGER>LEVEL:15
<INTEGER>MINLEVEL:13
<INTEGER>MAXLEVEL:19
[/UNIT]
NG+ Clones:
NG+
[UNIT]
        <STRING>NAME:sword_TESTm01NG+
<STRING>BASEFILE:media\units\items\swords\sword_TESTm01.dat
<INTEGER>LEVEL:60
        <INTEGER>MINLEVEL:58
<INTEGER>MAXLEVEL:63
[/UNIT]

NG+2
[UNIT]
        <STRING>NAME:sword_TESTm01NG+2
<STRING>BASEFILE:media\units\items\swords\sword_TESTm01.dat
<INTEGER>LEVEL:87
        <INTEGER>MINLEVEL:85
<INTEGER>MAXLEVEL:90
[/UNIT]

NG+3 (exception in Minlevel and Maxlevel, also has level_requiered:101 added.)
[UNIT]
        <STRING>NAME:sword_TESTm01NG+3
<STRING>BASEFILE:media\units\items\swords\sword_TESTm01.dat
<INTEGER>LEVEL:105
        <INTEGER>MINLEVEL:99
<INTEGER>MAXLEVEL:999
<INTEGER>LEVEL_REQUIRED:101
[/UNIT]

TL;DR:

Spoiler (hover to show)

Script inputs:

3d Model (Full access route)
Item Rarity
Name Tag
Item Level

Options:
Make Alternative clones
Make NG+ Clones

Full Example:
Input 3d Model: D:\Steam\SteamApps\common\Torchlight II\MODS\ITEM_MOD\MEDIA\MODELS\WEAPONS\_SWORDS\Sword_model_01
Input Rarity: Magic
Input tag: TEST
Input item level: 15
Make Alt Clones [Y/N]: Y

Result:
sword_TESTm01.dat
Created in:  D:\Steam\SteamApps\common\Torchlight II\MODS\ITEM_MOD\MEDIA\UNITS\ITEMS\SWORDS\

Code: [Select]

[UNIT]
        <STRING>RESOURCEDIRECTORY:media/models/weapons/_Swords
<STRING>MESHFILE:Sword_model_01
        <STRING>BASEFILE:media\units\items\swords\base_sword_magic.dat
<STRING>UNITTYPE:MAGIC 1HSWORD
        <STRING>NAME:sword_TESTm01
<INTEGER>LEVEL:15
<INTEGER>MINLEVEL:13
<INTEGER>MAXLEVEL:19
[/UNIT]

sword_TESTm01b
Created in:  D:\Steam\SteamApps\common\Torchlight II\MODS\ITEM_MOD\MEDIA\UNITS\ITEMS\SWORDS\

Code: [Select]

[UNIT]
        <STRING>NAME:sword_TESTm01b
<STRING>BASEFILE:media\units\items\swords\sword_TESTm01.dat
<INTEGER>LEVEL:19
        <INTEGER>MINLEVEL:17
<INTEGER>MAXLEVEL:22
[/UNIT]

sword_TESTm01C
Created in:  D:\Steam\SteamApps\common\Torchlight II\MODS\ITEM_MOD\MEDIA\UNITS\ITEMS\SWORDS\

Code: [Select]

[UNIT]
        <STRING>NAME:sword_TESTm01C
<STRING>BASEFILE:media\units\items\swords\sword_TESTm01.dat
<INTEGER>LEVEL:23
        <INTEGER>MINLEVEL:21
<INTEGER>MAXLEVEL:26
[/UNIT]


Great write-up. That sounds fairly reasonable to implement.

Not completed, but I got a good start on it.

https://github.com/RobJames-Texas/TL2_ItemDatMaker

Once it's further along I'll post a binary somewhere.

I can write some code to generate the guids as well. 

I noticed the legendary items do something a little different with the name.

   <STRING>NAME:legendary_greataxe01

instead of

   <STRING>NAME:greataxe_u01

so that will need fixed.

I was out of town for a couple of weeks.  I can get back on this now.

Ok. I think I took care of everything.  *...snip...*

Sweet man! This will help so many of us out so much! Does this board have kudos ;P

This should fix the things you mentioned:

https://github.com/RobJames-Texas/TL2_ItemDatMaker/releases/tag/v0.9.1

Ok, posting for a bump on this awesome tool. And also for a piece of advice for people using it.

Advice 1: The .dat files produced by this tool don't work right of the bat, you need to edit them to replace the "spaces"  before new lines for a "Tab", I didn't post this as a bug because is a common problem with text exporters to replace a "tap" for multiple spaces, I don't know if this is the case but It's my guess. Notepad++ has tools to do this, a "Search and replace" or "Space to Tab" both work.

Advice 2: The alternative clones and NG+ clones won't appear in GUTS to edit or in game mode, but work right in game when the mod is build, this is because the "Basefile:" line doesn't have the "mods/[mod_name]/" before the "media/..." naming of the directory, again a "Search and replace" works, or you can let this like that and edit the item files in notepad++

With that piece of advice, I recommend all people to use this awesome tool to make their items.

I didn't know about the tab thing.  I can change that easy enough.  I'm sure that I put spaces in there because for my programming I always use spaces instead of tabs.

Oh, as long as is not a big deal that would be nice. You're awesome @Vkoslak !