The "good easy" rear end swap for your 52 3100 would be a 1/2 ton rear end of the right width and six lug pattern matching your existing wheels. A rear end that only requires welding new spring perches as digg said (and a drive shaft). Beginning with the 1955 1/2 ton, the rear ends were open drive. I had a 1955 rear end in my 54 3100 for years and switched to a 1965 1/2 ton rear end when the 55 wore out. Think about the gear ratio you would like to have before you buy a rear end because you can save money and hassle buy getting the right ratio without changing the ring and pinion gears later. My 1955 rear end had a 390 ratio which was a good compromise between high and low end. The 1965 has a 373 ratio which is good on the highway but a little high for heavy low end pulling.
