My oil burning pig. Pics too!

I'm having a real tough time imagining how rings can push oil up into the intake, to puddle on a closed intake. PUDDLE. Really tough.
It's got to be through the guides or around them. Got to be. Or a hole in the bottom of the plenum, if it's doing it to all of the intakes.
If the rings are bad, a leakdown test will prove it,no need to disassemble it. But if the cylinder walls are washed, it could still lie to you.So if you are not satisfied with the results of the first test, redo it it with well oiled cylinders. Just let the pressure stabilize before grabbing the number.
If the rings were leaving excessive oil on the cylinder walls, it would burn and go out the exhaust. Sure on a late closing intake angle some oil could end up in the intake with a corresponding fuel-air charge, but it get's "sucked" back, either on the next induction cycle as part of the next charge, or it goes into a different hole, shortly following as part of it's charge.
Black oil in 81 miles goes to a very fat fuel charge,and definitely speaks to rings, maybe. If your carb is fat enough to wash most of the oil off, then the rings will wear out really fast. Or if the oil scrapers are doing too good a job, then same thing. Don't blame the rings,yet. And if your carb IS that fat, it will wear out the next set just as fast.
So I would start with a leakdown test; every hole , dry then wet.
Next I would dry up the carb. I would prove the float valves are working, and that the float levels are correct. Then I would defeat the power valve circuit. And of course I would sync up the Tports, and give it the ig. timing it wants.

Since you didn't like my first two tests, here is test number 3. Pick a valve that you thought was the worst. Put it's piston to the top on it's compression stroke and remove the intake spring and seat. Leave the seal on.Clean the head surface thoroughly around the outside of the pocket. Build up a dam with modeling clay, to a height higher than the valve seal, by about a half inch. Fill the cavity with some very light oil, like sewing machine oil. Pull the valve up.Mark the level.Let it sit overnight.