I am currently painting a 1974 John Deere 830 tractor and have been pretty impressed with the enamel I am using on the thing. Its called BPS or Best Paint Sold for farm implements and is like $20 for a gallon. You can add hardner and thin with a bit of Naptha.
Now I am SERIOUSLY considering painting my 72 C10 with the stuff. I am not keen on JD green, but I think I am going to go down to Tractor Supply and see what colors are available.
Paint is really hard and with the hardener in it comes out pretty shiny.