Marv:I tried to reply to your latest post on the E setups, but couldn't do it. Apparently I can start a new thread. I don't know what is wrong, I'm not a computer guy.
Anyway, the '56 dual four manifold is a different casting than the '57. I would guess the '57 manifolds were easier to cast and machine, therefore cheaper. The '57 manifold moved the carb flanges forward a little, I would guess to provide clearance for the larger '57 distributor. I have a copy of an ad from a manifold/carb restorer that said 102 of the '56 setups were built. I also have a copy of a letter to dealers, offering left over kits at the dealer's cost of $100!! I still have my '56 setup that I used to race on my '56 Bird.
John