Got some 3m safest stripper the other day to strip the paint off the side art. Wow that stuff kicks major butt! The paint comes right off, but it doesn't do a thing to the vinyl. I use a cheap ice scraper to get the paint off and it works perfectly. Literally takes 1 minute to apply stripper, and a minute to remove after an hour or two. I've uncovered the top part of one side and the side art is in good shape so far.
If anyone else has an old cab with possible original vinyl underneath paint, I highly recommend using the safest stripper stuff to see what it is.
I'll get some pics up this weekend probably.