79 Dodge D150 318 to 76 dodge sportsman rv 360 1ton dully chassis.

I agree that is tough to read. My take is you are building a truck for heavy hauling. Leave it alone. The RV was basically a heavy truck compared of course to a 1/2/ 3/4T so leave the chassis/ engine/ rear axle alone

Rear ratio will depend on weight hauled, cruising speed, and tire size