Are you planning on keeping this truck in a climate controlled enclosure? The two coatings which you have mentioned are not very durable when exposed to the environment.
Cadmium, in particular is classified as a sacrificial coating, in that it gradually dissipates over time while the metal under it is protected. The problem with this is that once most of the cadmium goes away, the metal under it will corrode. Gold zinc chromate is even less durable. Both of them look great in the dealership showroom...
Hopefully someone who knows about NAPCOs will come along and answer your specific parts coating questions. There is at least one website online dedicated to NAPCOs which may be a better source for you.
