New 4x4 conversion questions

[72kool]

I have gotten alot of good info from this forum but need help still.
Every year around this time I get the itch to have my truck 4x4 so I could is it more. It's a 1972 GMC C20.

Ideally I would find a 67-72 frame and swap, but I can't find any.

So I'm trying to find a complete plan on the best way to do a conversion. It has coil rear springs currently. Can I keep those? What is the best donor vehicle to get every part from that I need to swap? What is the best transfer case and front axle to use? ( I can't afford a d60 around here)
Aside from changing cross members, and installing spring hangers, any other frame modifications needed?

I have found lots of info on this subject in this forum. Seen it done numerous different ways and different parts . Looking to find the best,most proven plan to accomplish my goal. Thanks alot!