Basically just remove all the guts of both trannys, then remove the snap ring that holds the output shaft to the rear geartrain. Do this on both and swap the output shafts as you wish, when you go to reinstall put the shaft into place and re-install the snap ring. Put them back together and then the final step is to swap the tailhousings. Replace the seal and bushing at the rear of the tailhousing when you do it.
1993 K3500- 4x4, single cab/long bed, single rear wheels, 4.10 rear end, F vin, Nv4500 manual, factory red interior.
Gone but not forgotten: 2001 silverado 2500hd CC/SB, 4x4, 6.0 vortec, 229k miles when I traded it.