In 1972 Mopar lowered the compression ratio on all car 340 motors to 8.5 to 1, that is in blueprint specification. Mopar never blueprinted any production motors so the average car motor had less than that spec. My message is to go ahead and buy good quality replacement piston for the 1972,73 car motors and check the deck hieghts, combustion chamber volumes and see what true compression ratio you get use the head gasket thickness to help achieve the compression ratio you want IHTHs