https://eoserv.net/forum/topic/23955
This should help you out a lot.
A basic example as well is this:
Find the difference from end to beginning of an item. Take that difference (I think it's 29 for armors, the topic I linked has an alternative way)
Say one ends at 2851, add 29 to that, that's where yours starts.
Find the armor before the one you added, in pub files, find that GFX ID, +1 it.
Go into gfx 23, find the final item, find what that icon number is in your pub files, and +1 that, adding in the inv/drop view for your item.
That should set it.
I'm terrible with English, and with descriptions, so apologies if it sounded terrible.