[GRX]

"It seems up to a certain year that all of the driver's side manifolds had the divider, both center dump and rear dump."

"The Driver's side manifold has the #5 cylinder firing right before the #7 cylinder fires."

Ahhh ... makes more sense now that I look inside one of my logs and see the central divider extends almost to the outlet, essentially isolating #5 from the other three on that bank. Guess by the mid-70s performance was no longer a concern so it was eliminated. Makes me wonder how much performance was really gained with the ra3 manifolds and their 4 internal dividers isolating all the pulses.