Oh,
forgot the muffler will have to come off.
I prefer to remove the manifolds with the muffler attached to them @ the heads, because the muffler is easily damaged if trying to knock it off the exhaust manifolds.
Heat the manifold nuts up or they will twist off the studs, caution here.
Some prefer to take the muffler off the manifolds to prevent this, it is your call.
Luck!

Gents,
I started disassembly to fix the low oil pressure.

I used PB blaster on the muffler and I was able to knock it loose and remove it. Then I removed the PTO with a gear puller. Anything I should do to the PTO while it's off?

The rear cover came off easy enough and the spring, ball, and sleeve are intact. The spring is exactly 1" long. Is that correct?

I took the plate off the oil pump and the rotary gears look OK to me. See pic. I removed both gears and gave the shaft a tug and twist. It doesn't move. Should I turn the crank and see if there is a flat spot on the oil pump gear?

Is there anything else to look at?

Oh, and BTW, I picked up a can each of "Majic Tractor" Cub yellow and IH white from tractor supply. If the cap is any indicator the IH white is a perfect match. The yellow also looks close but hard to tell since it's dirty and faded.

Rob

Turn the crank, see if the oil pump moves.

TSC Majic paint is about the worst crap in a can ever sold. If you have not opened the can take back and get your money back.

What he said. I used it once on a crappy project i didn't care about and it was still wet a week later.

I cranked the starter a few times and the pump spins every time. Fished a wire down the oil switch hole to behind the allen set screw to ensure no blockage. Fished wire from pressure relief hole to oil pump output passage and it's clear.

What's next? I'm starting to get a bad feeling about this.

If the pickup is plugged maybe blasting a solvent down through the oil pump will clear it. I'll try anything.

Couple of things , just thinking out loud here.... Could the oil pump simply have lost prime? A friend of mine had that happen with his chevrolet. He packed the pump (which was new) with vaseline or grease or the like. and it built up pressure fine.
Since you have the cover off of the oil pump, is it possible (providing you have some oil in the crankcase), to put a suction (like with one of those vacuum brake bleeder vacuum tanks) on the open gear of the oil pump and see if you can suction oil up from the sump via the internal passages and oil pickup?
What do you think?

I think to make sure it is turning, you need a little resistance to the shaft, while turning over.
Remove the inner & outer rotor and put slight resistance on the shaft with a rag
pinched in your fingers, as it turns over.
That should tell if the gear is indeed pinned to the shaft properly.
As far as primed, the suction screen is in the bottom of the sump and the pump is almost that low so it should prime itself.
IIRR the drain plug it under the suction screen, so it should self clean when oil is drained.

The good news:

I spent all Sunday morning working on Gracie (my cub, not my neighbour;)) I replaced the ammeter with a volt meter for a few reasons. Now I can see what the resting battery voltage is. If the voltage dips below the resting voltage I know the battery is being drained. If it's above the resting voltage the battery is charging. An ammeter has never been very useful to me.

I also added an oil pressure gauge under the hood. I prefer it under the hood to minimise the length of the oil tube. I still have the light as well.

The bad news:

I still lose oil pressure above idle. I grabbed the pump shaft with my fingers and held it while cranking and it did spin. I tried to pull oil up to the pressure switch with a hand vacuum pump but I got tired hands and no vacuum. I primed the oil pump by dumping oil down the oil switch fitting and cranking it until I saw the bubbles stop appearing and the oil started to come back out the fitting. I even over filled the crank case a little bit.

At idle oil bubbles flow toward the gauge and the light goes out, but fast idle the bubbles move away from the gauge and the oil light comes on. Gauge never reads above 4 psi.

Ol'George said the oil pickup screen is above the drain plug so I stuck my pinky in there and also looked with a flash-light. There's no screen, just a hard, smooth, metal surface. Could someone have split this engine and forgot to install the pickup?

Yes, possibly. Could also be installed incorrectly. Had a guy on here one time that had an issue like you are having. I can't recall if the sump wasn't installed right, or it was plugged. Either way, splitting the crankcase seems like the next solution. Unless you know someone with a borescope. Then you might be able to see what is wrong without splitting it.