If you have a regular 3500 dually, then you would need to find a single rear wheel axle from under a 3500 as 2500's got a slightly different axle under them(it is said that 2500 Suburban's with a 14 bolt 10.5" full floating axle is the same axle, just different mounts as the 3500 single rear wheel). You'll probably also want tge springs from a 3500 single rear wheel, and do away with the dually's overload setup. If you have a 4x4, then all you have to do up front is remove the dually adapters/spacers(these will normally bring a few dollars used), but if it's a 2 wheel drive you will have to swap rotors, calipers, and pads( single rear wheel trucks use rotors that are 1.25" thick while duallys are 1.5" thick. You can use the rotors, calipers, and pads from a dually on a single rear wheel 4x4 since the rotors interchange, but you cannot get the 1.5" thick rotors for a 2 wheel drive single rear wheel truck). Out back the dually axle will have 13x3.5" shoes with 1 3/16" diameter wheel cylinders while a single eear wheel 3500 will have the same 13x3.5" shoes, but only has 1 1/16" diameter wheel cylinders. The good news is the 1 3/16" wheel cylinders swap right in place of the 1 1/16" ones to keep somewhat acceptable rear braking. Theres some other differences, but that I think will amount to much.
Now if you have a factory cab and chassis model, or one ordered as a bed delete, it's a completely different ball game. They used narrower frame rails in the back, and different rear spring mounts and such.
