Latest update:  I have tried oiling the shift shaft, putting the shift lever on and trying to move it and tapping on the case to coerce separation.  No progress.  I'm also running a razor along the case.  the clutch cover had a pretty sticky gasket.  It's difficult getting around the bottom.  I have removed engine mounting bolts except for the rear one that cannot come out because it is behind the cover we are trying to get off.  This does allow me to angle the engine up to access the bottom of the case.  Hopefully I can get to that today after I "lay her down" to get a gravity assist for the oil to get around the shaft better.  What are thoughts on adding heat into the mix?

Just thinking what i'd do in desperation & without looking under mine i'd suggest running an angle grinder with a thin cutoff wheel & carve a slot or two slots & break the piece out in between slots.
I say that because it isn't a super important piece & even with a bit missing it'll still give support of sorts.
Then that might relieve it somewhat & get some oil right at it.
Wish i could find my pics of the same problem on one of my similar bikes with that problem.

We have SUCCESS! The culprit was in-fact the shift shaft and corrosion around it that held up the show. Much penetrating oil, loads of love taps and a few choice words finally got the cover off which allowed me to remove the engine. Now to get in there and see whats keeping other stuff from moving. Stay tuned. I'll be back with another topic, I'm sure.

Thanks for the assistance and working knowledge.