Espo, the Rochester g series (1g, 2g, 2gc, 4gc, etc. ) was GM's most commonly used carb from the early fifties up to the late 60's. The "c" signified choke mechanism, by the way. The number designation was the number of barrels (or venturis) in the carb, so 4gc was a four barrel carb. The 4gc was available up to 1967, I believe. At that point, it was replaced by the quadrajet with the huge secondaries. The 4gc secondarys are roughly the same size as the primaries. Thanks, Ron.