Joe wrote:
Thanks for the advice on all this, everybody. Tons to consider with all this, and lots of "damned if you do, damned if you don't."

I did confirm my "tick" is coming from the valve with the makeshift shim with a stethoscope. It seems to have the telltale signs of having collapsed (lifter stops spinning intermittently, all the others continue to spin). When the engine is off, the valve spring can be spun by hand. The last time I did a compression test (September 23, 2022), my compression numbers were all 87-92. The car truthfully runs much better now than it did then, but there've been numerous other things I've done to it in the meantime. I doubt the compression numbers have changed. I've put MAYBE 200 miles on the car since I bought it. I've changed the oil maybe four times? Doubtless it needs a proper date with a good mechanic. I'm currently running full synthetic 10W-30 (Amsoil if that matters) without additives. Gas is ethanol free with some MMO. Seems to be what most everybody uses.

I have a couple NOS hydraulic lifters on order, along with a side valve compression tool, along with another tool for installing the keepers. My plan right now is to start by addressing the one lifter I know to be problematic. If I can get the hang of disassembling and reassembling everything with the problem valve, I'll dive into the others, working to clean the lifters and lap the valves. If I find I'm hitting my mechanical limit and feel like I'm going to make something worse, I'm going to hit the pause button and call in more experienced hands. It's a bit by bit approach, but it's where I am for now. Again, I appreciate the advice, everybody. Thank you!