As usual, something jumps up and bites me in the butt JUST before the deadline!
I didn't like the initial start-up exhaust smoking that failed to clear up but instead got worse after a couple of nice romps around the neighborhood, so I pulled the top end off. Head gasket fine.
Pulled the jugs off and took them, pistons & rings, and my complete 880 kit over to the machinist with Dreer's specs in hand, and sat down with Miguel and his micrometers. We determined that the three-piece oil control rings were to blame.
So, I'll go ahead and just use all of my new rings and start over. Should have it running and proven by tomorrow evening (base gasket on it's way overnight).
Meanwhile the welder is doing a couple of last-minute refitting adjustments to my custom adapted Mark III rearsets, and I took the afternoon to fabricate & install the new meter bracket.

Punchist items can now be counted on one hand...