I've got old 8R19.5's on mine. Check this site out if you want to get the nice (but expensive) 19.5 tires and rims. http://www.ricksontruck.com/wheels_gm_drw.html

There are other places that can sell you steel rims cheaper. I'd love to have those 285 /70R/19.5 tires and rims. Those extra inches in diamter will help your speed out as well.

Are your current wheels hub or lug centered? What is the center hole diameter? What is the wheel offset? Do you have 1/2" or 9/16" lugs? You'll need to know this kind of stuff to get new rims.

My 1958 Chevy Apache 38 1-Ton