If you want to confirm what they looked like you can see all the Cameo models 55 - 58 at
www.chevrolettruckservice.com/. As stated there is no sure fire way to identify a Cameo, but there are a lot of clues. Look at the door data plate in the left door jamb to see what is listed for RPOs if anything. In some cases the Cameo was identified on that plate as an "RPO (regular production option) 447" or just 447. Also, you can check the paint code to see if the code was really a Cameo color combination. Sometimes 3124 was penciled on the firewall, but not in all cases. The unique bed, bumpers and ends, chrome work, deluxe cab etc. including the 57 can all be duplicated, but, and a big but, it can get to be a costly thing to do. The 57 has "Cameo" script on the bed and "3124" in the spears most times. Lots of things to look for, but of course over 50+ years many things can be changed as well. Helps too if there is some paperwork trail with previous owners. Good luck with it. Dale
