You're expecting this to be way too simple. Even very similar pick-ups will have different payloads due to having more or less options on the truck. Your C&C has a longer frame, possible a heavier frame, dual fuel tanks, a larger rear axle (I think, maybe not on a gasser), and they used to have a rear anti-sway bar that the pick-ups didn't get.
There are certain options that are absolutely not available on a C&C truck like satellite radio for instance. Your truck probably didn't come with a spare tire or a winch to hold it but a dually comes with both.
So, bottom line is, there are a lot of differences and you can't just assume anything.