My first entry to this forum. Hope someone is able to help- I am in the process of rebuilding a '69 RA III 400 from a '69 GTO convertible using the 4-bolt block and #48 72 cc heads. Seriously need to get the compression down to at least 9 to 1. Also believe i should zero deck the block because have heard this adds to the detonation problem... that would even possibly raise the compby Judd Wymer - Pontiac GTO Forum