The Heads on the 468 are standard W9's done by Champman, they flow in the 360 CFM range at .700 lift through the intake and throttle body. The minimum cross section on W9 heads is small in comparison to the W9RP's.

The heads that are going on this 420 cid motor are W9RP done by Curtis Boggs at RFD and they flow well over 425 CFM at .800 lift and continue to flow better up to 1" lift. The W9RP will not fit on the 59 deg motor because the rocker offset is not enough, the pushrod will hit the head.