78 was the last your for the 750 sohc. the 650 went to 82 but used something similar to the 750 dohc for ignition.
As for transplanting, my guess is you will need the whole unit from a dohc and may need to rig up an adaptor or mod the shaft. May just be better off with a dyna-s or a boyer-bransden if a stock engine. If you got it modded, then a dyna-2000 or a cycle-x optical ignition.
I use a dyna s and just keep the points plate to take with on long trips, just in case.
The ride IS the adventure. The destination is just to get gas!