LOL
I talked to wayne and some others on facebook the other night and there seems to be plenty of ways to skin this cat.
Wayne suggested cutting the floor out of both trucks and welding in the floor from the 6.0 into the 76, that way when i put the cab on the frame the cab mounts do not have to be changed and the master cylinder, pedal, transmission tunnel, ect all bolt up in the factory type location. My only reserve about this is the positioning of the cab on the frame in relation to how the front tires will line up with the fenders. but i think with some measuring it will be ok, Also the factory 76 dash might not fit the same but i am not sure