I've used Jerry's book (Its so tatered now I think I will need to grap an other copy soon) and photo's of low mileage GM vehicles (of the same vintage of car being restored) collected over the years. But, if you want a quick reference on the WEB - check this site out.
GM Body Detailing Site (OLDSmobility)
Somebody should do something like this for our Chevy muscle.
Good Starting point.