Aftermarket wheels and tires suggestions for 1970 C20 with Disc brakes

[jjmaple]

I am looking to replace my stock rims/tires on my '70 C20 (3/4 ton w/ 8 lugs wheels). I plan to upgrade to disc brakes on the front, so that should be taken into account. I will be towing with this vehicle, so would like to retain the stock ride height. I need some advise with the following:

1. What is the largest rim/tire size I can go with without clearance problems? The truck has stock suspension and will not be lowered.

2. Any suggestions as far as wheel/tire vendors? I am located in Southern California.

3. Do the aftermarket rims need to have an offset?

4. Any suggestions as far as aftermarket disc upgrade kits for a '70 C20 (3/4 ton with 8 lugs. I would like to go with stock height spindles).

Thanks in advance for the assistance.