1972 Wheel and tire questions

[superflydude]

I have a bunch of questions I hope you guys can help. I just got a 1972 K5 and I want to restore and redo a lot of things. One thing is I want to change the wheels and tires on it. It has a 33x12.5 on a 16.5 rim now. I want to get a bigger rim but i don't know the bolt pattern. Can anyone tell me what it is? Its a 4x4 also. And if I put it on 35 tire with 18-20 inch rim will there be steering issues or will it hit the wheel well? Will i need a lift kit or spacers? And if so how big? Last question is does it make sense to put a 20inch rim on or would i be just as good with an 18 if I'm mounting 35's on it? Thanks alot -Mike