[JoeG]

Hello musclcar, There was a C-3B Edelbrock hi-rise manifold for 283/327/350 to be used with the 3bar.holley--------I'm guessing on yourC-3BX, your plenum divider has been completely opened ,instead of just a notch cut for the 3bar. sec.throttle plate------------JoeG
The first advertisement I found for a C3B Edelbrock manifold is '68.