[justcuz]

Most are what you mentioned. Body shells are the same. Grilles and hood are different. Mostly cosmetic on the body.

Running gear wise exactly what you said, better t-case, open knuckle front axle with disc brakes. They would both have the same 12 bolt rear axle if 1/2 ton or eaton if 3/4 ton.
If it was me I would pick the one with the best body. All the driveline stuff is easy to swap in.
If your not handy mechanically then buy the 72, it has the better front axle and t-case which are more plentiful from a replacement part standpoint.

My personal opinion is it is easier to swap an engine and transmission than convert an eight lug to a 5 lug. 8 lug to 5 lug requires a lower control arm change to the smaller 5 lug ball joints and you have to go to smaller u joints at the rear axle as well.
A six cylinder 4 speed to V8/auto will require V8 motor mounts and a trans crossmember, plus change the front of the driveshft from a u joint to a slip yoke. The six/4spd will have a bell housing crossmember to support the transmission, for the auto you need a tailshaft crossmember.