I don't know where you got your 9.5 to 1 number from with the 64's unless there has been some moderate milling on the decks. 64 heads are 87 cc which equates to 8.6 to 1 on a 400.
64 heads are a great choice for a 428 or 455...but not for a 400.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.