While you have the stuff, if he has the jack to buy the stuff AND (as is obvious) is a man of principle, it is MORE respectful of his beliefs IMO to do a fair exchange.

I'd go with Option C, promptly install it, and show him how much you enjoy it. You can also help build the truck with him so it doesn't sit waiting to be done. Since the whole thing isn't about money, make it about building a kickass truck with him.