Opinions sought on odd engine knock

Since compression is fine, and you see end-play, I would change the main bearings (one is the thrust bearing). That would be many times easier than a full engine rebuild. Change the rear seal while down there. I did this in my 383 from below. I did a full ring & hone job (removed head & pistons), but you don't need that.

You simply push the top of each bearing shell around the crank w/ a blunt screwdriver. I expect this works the same in a slant. I pushed a rag w/ ethanol around the gap to clean oil from the block surface to insure the bearing shell will stick, though a tab on the bearing keeps it from spinning. Same deal for the rear seal, if you have the split rubber type. If the original woven rope, I think it just pulls out. There is a special wire puller to re-install a rope seal, but nobody does that today. Good these engines aren't like my 80's M-B diesels that have a steel pin that locks the rope seal so you can't pull it out, frustrating owners. Ideally, use plasti-gage to check the gap, but you could just measure the thickness of each old bearing to insure you don't have any special thick ones (for over-ground crank position). That is rare, and your block should be stamped (behind alternator?) w/ a Maltese falcon mark or such if an under-sized crank. That was a way for the factory to salvage an incorrectly forged or machined crank. Also, easy to change the rod bearings while in there. Do all one at a time, to support the crank and not risk swapping caps. The caps should be marked for location and orientation, or do so if missing. With new bearings, you should see higher oil pressure.