I would leave the firewall body color- supposed to be that way. The inner fenders and radiator support are supposed to be low gloss black. However, paint it whatever color you want. You could also paint the motor to match the truck, just get some PPG ALK paint mixed up to match. This all depends on your tastes, not ours, personally I like the original look on these old trucks. If I wanted to customize things, I'd make everything the same color to give it a clean look.
