high compression

OK I have been doing this for a long, long, long, time, just pull the heads. You read the spark plugs, and you read the valves with a scope then there is nothing else. If your leak down went OK, plugs look good, I would bet you popped the gasket between 3 and 5 on the thin spot between the two. I would get a straight edge, pull the heads, and check the block and have the heads magnafluxed. The PSI doesn’t concern me it’s the drastic difference between all 8 that have me concerned. You can pop the gasket in the thin area and never see a bubble in the coolant. When you reassemble the engine start an engine log, thickness of head gaskets, piston type (Flat, two valve reliefs or four, small dome, medium, large), head casting numbers, valve size (gasket type, head type), CC heads (It is easy to do with Plexiglas, a $3 dollar Beeker, and oil “not alcohol”, and a little grease, cost $20 bucks). The point is you should have a book with everything you have done to the engine, and all your experiences. It will save a lot of headaches for a few minutes and a $3 book, just saying. When you put it back together use a tri-metal-gasket they are expensive but worth every dime.