Tech Help on a 1980 Mercury 200HP 2.4

[BuilderFL]

Due to a water pump failure, my engine overheated and hoping to make it back to port, I continue to navigate until the rubber grommet on the temperature sender melted and started to smoke. Shut it off and it did not start again. Compression tested all cylinders and got about 65 psi, way below the 120 psi I should be getting, but then again, all of them at 65 psi, very interesting. By the way, I do the compression test with all plug out. Inspected the pistons and found no scoring on the sleeves. Replaced both cylinder head gaskets and still the same compression. Any suggestions? Thanks!