The bigger truck likely has more value as a whole. If you keep the cab then the leftovers like axles, frame, and so on you'll be lucky to get more than scrap for.
Decide what you want out of the two trucks. If that means parting out the big truck to feed your small one just don't expect to make much money on the other leftover parts.
If you want to keep the big truck complete and part out the small one that's certainly a fun option too! Or keep both and keep looking for a cab for your small truck.
