Need help for tire size

[JKNAPP285]

I just bought a 72 c10 and need some help figuring out what kind of rims/tires i would need for it. The truck has the 5 lug conversion from a 78 c1. what back spacing and offset would you recommend. I would liked them tucked slightly and would love the look of a 20 in rim. I also will be lowering it 2 in the front and 4 in the rear. Any help would be greatly appreciated. If there is already a page for something like this subject could you point me to it!

Cheers, Jerry