Cylinder #7 down on compression

Can you give us the specific spark plug number. It’s on the plug.

Not really sure the point in cleaning off the pistons. If you insist, do the grease thing like mentioned earlier.

I’m always amazed when people are surprised that their 55 year old motor doesn’t have original parts in it. Nearly all piston replacements in the late 70s, 70s and 90s were low compression due to available gas.

If it blows 150 psi when you are done, it’s probably because it has a replacement cam too.

Consider a shim head gasket for installation.