Early vs. Late dusters

75, for many reasons. It's running and driving being a big one. But even all else being equal, I'd say the 75. Caveat: if the engine swap on the slant six K member is a hack job, run!

The advantages are many: BBP discs, probably an 8.25" axle (72 could be a 7.25"), 3-point belts, electronic ignition, the folding seat.