Ok, your 53 should have 4.11 gears. If you measure the diameter of your tires to the closest inch, you can take this info to an on line rpm calculator. I like the calculators over at 4lo.com.
I believe, but might be incorrect in this belief, the 235 can be run all day long at 3400 rpm. If possible, I would try to gear the vehicle to be around 2200-2400 at cruising speeds.
