Rocket,
Here is what I would do. I would buy the half ton and then swap in the 3/4 ton parts you want/need. This would be the option as long as it is cheaper, it wouldn't make much sense to save money on the half ton and then turn around and spen more making it a 3/4 ton.
As far as parts I would put a full floating (8 lug) 14 bolt in the rear end. This can be sourced from a 73-87 truck. Since it is a rear end it can be a 2wd or 4wd truck that you get the axle from. Make sure to get a gear ratio you want.
In the 73-87 body style there are three eight lug front ends. There is an 8 lug 10 bolt, an 8 lug Dana 44, and an 8 lug Dana 60. If it were me, having owned and operated the 10 bolt, I would go for the Dana 44. The only way that I would use the Dana 60 is if I was planning on building an off-roader. Otherwise it is just overkill.
As long as you get the motor, tranny, and transfer case that you want in the half ton then I see no reason no to swap in the newer axles to increase your towing capabilities. You could take the springs and hardware from the newer truck and just toss it under yours. I know that swaps like this are done all of the time by off road guys, so I would check some off roading magazines and websites to see what they have done. Good Luck.
Kyle
