Nice truck, I have also a Suburban k20 -82 and it has 33/12.5-16.5 tires. I am getting 255/85-16 on OEM steel wheels later. If I ever do any suspension modifications it would never be more then 2 inches.
Here is a link to my truck:
http://67-72chevytrucks.com/vboard/s...d.php?t=567608