The engine was built a long time ago and i did not build it.The guy who built it for me said that he used a thicker head gasket to reduce compression so it would be better on the street.I have no idea how far the piston comes up in the bore.I have never had a problem with overheating,detonation on pump gas but I did have a problem with engine shut off.I don't know if it was the MSD ignition but the car would not shut off if i took the key out.I later fixed it by starting the car and while the car was running flip a toggle switch to cause the alternator to charge the battery.That toggle switch is a switch that turns the charging system on and then can be turned off after the engine is running. I never measured cranking compression.Would that give me a estimate on what my final compression is??? I have never heard of Gear Vendors Over Drive on back of a Muncie-M20.My Muncie M-20 sometimes jumps out of gear so I would not use this transmission to upgrade.How does that work and how much money for there overdrive???I know that Richmond makes a 5 speed and 6 speed but they are really expensive.I know some guys are using the 5 speed Tremec and T-56 6 speed trans in there low geared big block car today???