Need help with rim size

[jjmaple]

I have a '70 C20 that I would like to replace the stock rims with aftermarket ones that will provide me with the necessary clearance to install first disc brakes. My questions are as follows:

1. What is the widest rim size on a 16" wheel that I can go without clearance issues? The truck is not and will not be lowered.

2. Do I need a specific offset or is "0" offset the way to go?

3. I have seen mention that any '65 to '09 Chevy/GMC factory 8 lug rim will fit my truck. Is this true?

Thanks in advance for your help.