[BRENT in 10-uh-C]

If I am reading the #1 post correctly, the knock has been in the engine since it was first rebuilt. Then upon a disassembly and inspection, a high compression head was installed. Since the knock has been there since the rebuilt engine was first completed, I think I would rule out piston interference.

As for the high copper, lead, and tin, ...these are items found in bronze, -and if the thrust bearing on the main was made from Bronze and then clearanced too tightly, this could be the source of those high levels in the oil.

Without being able to check clearances with micrometers and indicators, anything we say will just be speculation. Maybe it is one or more bent connecting rods, maybe tappet to bore clearances are excessive, maybe the line-boring operation bedded the crankshaft outside of being truly parallel with the cylinder case or even straight in the centerline.