Like you Paul, I'd love to understand the Holley carburetor I.D. system from 1956.
Looking at the '49 - '59 Ford Parts Text Catalog, there are twelve (12!) different four barrel carburetor stamping I.D.s listed for 'Bird and passenger car 292 and 312 applications!
Of these 12, two are specifically called out for 'Bird, Fairlane, and station wagon with standard or overdrive transmissions:
ECJ 9510-R
ECZ 9510-A
The parts list for these two carburetors is #35
Another two of the 12 are called out specifically for 'Bird, Fairlane, station wagon, and passenger car "special" with Fordomatic transmissions:
ECJ 9510-N
ECZ 9510-B
The parts list for these two carburetors is #36
Then there's a listing for another six carburetors that are for 'Bird, Fairlane, station wagon, and passenger car "special" with no transmission designation (I take this to mean 'any' transmission, i.e., standard, overdrive, or Fordomatic):
ECJ 9510-U or V
ECZ 9510-G or H
ECZ 9510-L or M
The parts list for these six carburetors is #37
The last four of the list of 12 are for 'Bird, Fairlane, station wagon, and passenger car "special" with no transmission designation (again, I take this to mean 'any' transmission, i.e., standard, overdrive, or Fordomatic):
ECJ 9510-Y or Z
ECZ 9510-L or M
The parts list for these four carburetors is #39
NOTE that the carburetors ECZ 9510-L and M are listed as being on two different parts lists, both lists #37 and #39
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Again, ALL of the above carburetor applications are for both 292 and 312 engines...
In 'efforting' to assemble a y-block dual quad set-up, I have gone out of my way to obtain two '56 single quad application carburetors with the same stamping numbers as a basis for necessary modifications. I've done this because I am suspicious of differences in passageway sizes or orifice metering openings within the different series of carburetors.
I have not attempted to wade through the four different parts lists that cover these 12 different carburetors to determine the parts differences. I suspect that it is more than just whether one has a dashpot or not.
Hope this info is of some help.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York