1973 340 issues.

I would really suggest you do the check with the air in the cylinder before pulling the head. Once you pull the head, you have lost the opportunity to pinpoint the problem better, and may be back to pure guessing.

IMHO, lapping the valves is not going to do much. It might bring up a few good cylinders a few more points but the guides are probably so worn by now as to render lapping useless. If anything is bad enough to drop #2 to 23-30 psi cranking, lapping is not going to fix it.

And those compression pills were in the same category toilet paper oil filters LOL