As I remember it Alan not much. The upper motor mount is different so that stops you from putting the later bracket assy. on the older motor. Not saying it couldn’t be done, just easier to go to the later motor. It wouldnt be a good idea to stop off at a 1973 either as it is a one year motor in regards to the stroke. Starting in 1974 the V-4 stayed the same piston, conn rod, etc till the end. The motors picked up the bigger center main bearing common with the V-6 motor in 1979, but most other things internally stayed the same.
1973 was the first year for MagFlash CD I believe they called it? Everything completely different from battery CD from before.
My favorite V-4 of all time is the 1978 85hp. It is the only small bore (3 3/8") with the later internal trim system. It was probably the most durable motor OMC ever built. Many are still out there running with original powerheads. Not an antique, but difinitely should be a "Classic" in anybody’s book!
Dan in TN
.
