I think the GHQ truck is the way to go. You could have a special run of 150 Peterbilts and 150 Ford L9000. The core frame/cab of the Peterbilt dump and logging truck will work. Both models have the same extended wheelbase of the cab/sleeper without the sleeper cast with the cab as on later tractor models. The Ford L9000 dump truck, garbage truck or cement should provide a good core frame/cab.
For my money, the logging truck is the way to go. Its fairly cheap and includes an extra set of wheels for the trailer.
Now if BOB was looking into purchasing a car line, I have heard that CnC was trying to sell their N scale division which included a Ford L9000, several Chevy trucks and a few vintage 50's vehicles.