OK, well the base gaskets are the same. Looks like both gearcases use the oring on the driveshaft. So, I see no reason why it won’t bolt up. But, I would keep the add on stuff with its original crankcase… So, if you are using the 77 crankcase, I would use its ignition stuff and carbs.
And yes, the 77 models had a bracket that all the ignition stuff bolted onto, the ignition stuff on the 82 models bolted directly to the head and block…
