You guys are mixing metaphors a bit.
Re: getting SPID labels made - I believe chipflyer will make a SPID for whatever model year truck you want. The trick is that YOU have to tell him what RPOs you want on the label.
Re: what RPOs you want on the label: you are correct - the possibilities are endless.
For 1976 and newer you can send your VIN and $50 to the GM Heritage Center archive and they will give you the actual invoice for your specific truck. This will include all RPOs and the pricing for those. Link:
http://www.gmmediaarchive.com/
If that does not work for you then your only other hope is to find an original build sheet in the truck somewhere (under the carpet, stuck in the seat springs, above the headliner, etc). These were to help faciliate the build and exist only in the truck (there were intended to be thrown away at the completion of the build and no copies were kept by General Motors).
If that doesn't work then you'll just have to use your imagination and make something up...
K