Find out what the 70's model engine is. If you look at the block under the motor mounts, and it has a 401 it would be a great power plant to start with. Other factors like rust, appearance, price, and if they even run should also factor in. But if they are evenly matched and the older model has the coveted 401 you will not be disappointed.
Wag Rebuilt 360, 260H, 727, Locked 44, AMC 20, 208, 31" M/T's, 4" Rustys, 2.5" Duals. SOON:SOA SF, 496, T400, Doubler, D60's, 37" M/T's <-TOY
Cherokee Rebuilt 360, 2" Duals, mostly stock. SOON: Hot Street 401, 4'' Rustys, 33" BFG A/T's maybe a T-case to get rid of Q-Track <-TOW RIG