GTX, I expect a copy of the original Build Sheet would be documentation enough?
That's a common misconception.
Having the BS is certainly a good place to start, but simply having the BS does not ensure an accurate tag.
Tag codes change year to year, plant to plant and even within the model year.
The BS does not tell you which codes go on the tag, what time of the model year the codes are supposed to appear on the tag, when codes are paired (IF/THEN coding) or even where on the tag the code is supposed to go. You still have to have someone with the right knowledge to accurately layout a tag.
The BS does not tell you unique tag data like Lynch Road Gate and Base codes.
The BS does not tell you which codes supersede other codes on a tag (the Jefferson plant superseded a lot of codes)
The BS does not tell you plant nuances like when the '69 Hamtramck plant transitioned from stamping END on the tag to EN1 and EN2.
The BS does not tell you when certain codes appear for certain models at certain plants. Different plants coded differently.
Making accurate tags from scratch requires a BOATLOAD of homework that the vast majority of tag makers NEVER do. To make accurate tags, one has to learn every tag detail from every plant from every time of the model year from every model and every body style.
Plenty of crap tags have been made even with a BS available because the tag makers doesn't know what info to use from the BS or when to use it.
But, there are plenty of people that will take your money, stamp some codes in a piece of metal and sell you something that resembles a factory fender tag. Some of those vendors will probably be listed in this thread by well meaning folks.