On tearing down my basket case '86, I discovered  that there was a nice sized hole in the bottom of the crankcase.  The po had covered the hole with a load of some kind of semi hardening sealant.  I'm wondering if I can transfer the internals, which all look good to any year crankcase halves or if I need to stick to a specific year range.

thanks

I don't know what the differences are, but there are a few.
Maybe not the case, you should examine them closely.

A while back, someone wanted to exchange the final drive shafts, but the ones they had gotten where different and didn't fit.

So I'd rather buy a complete lower end, case and guts.

If the bike was mine and I was going to be putting miles on this bike - I would make the upgrade to a 5 speed engine.  Be sure to move the rotor and stator from your 86 onto the replacement engine so the timing and electrical connectors are compatible.  You will also need all the transmission internals as the gearbox is different.