First are both of these trucks long beds and have the same cab configuration?
I am assuming yes, so as long as those match up you are good for the swapping things between frames. The engine and drivetrain though that is different. You will need to swap the front engine cross member to the 4wd version if you are using the 2wd frame, as well as make new mounting holes for the 4wd transfer case mounts/skid plate on the 2wd frame.
Be sure to use and keep the wiring harnesses the same from each truck, because of different years and different options things can get out of sorts with locations of wires and connections if you try to mis-match them. Keep them together as one unit.
On your frame concerns, I wouldn't worry. The half ton frame in good shape will do fine for the type of towing you are doing. The 1 ton frames are technically different starting in certain years. Someone will chime in with those facts as I have never had the funds to really care since I stick with single cab short beds or tow that heavy to begin with.
As I mentioned earlier if you are body swapping might as well try to put as much sound insulation in the cab/doors as possible. This will give you the best ride and comfort on those long hauls.
CCB and 440 above are right on the engine recommendations, good cam, intake/carb, headers will be your ticket to low end grunt on the cheap. If you can afford it heads will also be a huge improvement from the stockers as well.
Be sure to do your research on some small block builds on the net and actual low end dyno numbers, not the high end fancy stuff with big jumps but the flat torque curves at the hit. That is what you want.
Neil
