The '78 engines are quite a bit different. The carbs, hoses, airbox, head, and pistons do not interchange directly with your engine, so maybe think twice about the exchange? The oil tanks are different (as are the hoses) and the wiring harnesses are distant 2nd cousins, even the fuseblocks have opposite genders on their plugs!
I would have never guessed that. My plan is to run the '78 engine complete, then eventually reinstall it back into the parts bike, which is pretty much complete and has a clean title.
I hate to chop anything up, which is one of the reasons I bought mine already built and messed up. The '78 has been in someone's shed since 2005 and sounds tough. I will swap parts around between the two bikes a bit, but eventually build a cool bike out of the '78 and sell it. It should a fun project that my boys and I can do together.
I may change my mind, and piece the engine I have back together. I'm not committed either way yet. I really appreciate the advice everyone has given me on this. I suppose I should start a thread over In projects, since this has rapidly progressed into just that ha ha.
