Small Block & Big Block Chevy Specific - bbc head casting numbers what are they

3994026 rect port i no there from 71 ls6 425 horse 2.19 valve but i see places saying open and closed chamber how do i tell and how can i find out how many cc runner is?

from the mortec website that i found in an archive

3994026....71......rect...OPEN...454 LS6, 118cc chamber

Nhra website lists runner cc specs for all legal heads.

Intake runners are 323 CCs and the exhaust are 127 CCs

Thanks pretty stout set of heads 2.25 intake valves to.