Head Gasket Thickness???

If You Just Use A Thick Gasket You Will Lower The Compression Less Than If You Use An Extra Thick One. A Super Thick One Will Lower It Even More, But If You Really Want To Lower The Compression Use A Super Duper Thick One. Depending On The Quench Situation In Your Combustion Chamber You May Actually Raise The Possibility Of Detonation By Using A Thicker Gasket To Lower The Compression Ratio.

You're easily over 11:1 with a 64cc head and most any gasket that will fit a 400. With a typical -7cc piston, .040" quench and a 64cc head you're right at 11.4:1. Add .025" for deck clearance and you're down to 10.75:1 but you're flirting with detonation due to the loss of quench effect.