I use a similar setup on my 1Ton only I do have the 4:10 rearend. If they can give you the specs, you will want to keep the setback on the rims to about 3 1/2". The Tire Rack site will give you the numbers on both tire sizes so you can compare. If you multiply the revs/mile by your rearend ratio you will get the RPM at 60 mph.