A bit of a head scratcher that the two issues are even coinciding...........I've/others all have lost reg's on these blocks where the voltage was jumping up too high (tach may have been freaking too) and the motor still ran smooth. This to me sounds like a ground issue or stator issues because the two systems should remain mutually exclusive with the exception of a common factor of either, 1) ground or 2) the stator. Given that, I guess I'd start with a few fairly quick and easy tests .......
1) Check, recheck and tighten ALL the grounds lugs (and associated wiring as you go) on the block, try and run it again. If problem continues........
2) Disconnect the 4 yellow wires (tape/cap them off) and try and run it again.
My thought here, not only will this remove the reg's (should be a moot point) out of the picture for the moment, is that perhaps when the stator is getting hot/heating up (which it does) with normal batt charge load/s via the loads through the reg's, the stator's enamel could be cracked and expanding and a short to ground or across winding's is occurring in the winding's.
Thus, disconnecting the 4 yellow wires and running should allow the stator to run almost stone cold and perhaps help determine if it's heat related stator issue.
Vibration of course will still occur and it could still drop out and I guess at that point, I'd pop in a new stator.