Jerry,

Both pushrods will be at the same lift even when the cylinder is not on the compression stroke

Nope. When the piston is on the intake, the exhaust pushrod will be higher, since that valve is closed.

You may have lost galley plug at end of that lifter galley and hence lost oil pressure to lifters resulting in that condition.

Good thought, but I didn’t mention that I had 50 psi of oil pressure. However, I did mention that all the other lifters had some travel when at TDC.

Can you see if the dogbone is holding the lifters in alignment?

Nope. No way with these heads without pulling the intake.

And what did that spark plug look like?

Normal. I didn’t drive it very far after I had the problem.