...The date codes on the two air cleaner bases I have are 6E (1966 May) and 7A (1967 January).
FWIW, to help out ANY reader regardless of the OP's needs, a 67 air cleaner lower housing is designed differently for the 4300 carburetor than it's predecessor 4100 version. (This should be true on all three 1967, 4300 versions I am aware of). Jim, you should notice the different-shaped bottoms on your 7A date stamped example when compared to your 6E stamped example. Perhaps you could post a picture of the different "bulge" you should see on your 67 version. My understanding is that the 4300 version fits on the 4100 version (66-older cars) but not the other way, the older does not fit the newer 67 4300 applications because it hits the 4300 carb up front near the filter area.
ALSO: FWIW, there are 3-67 version lower bases I know of outside any Hi-PO applications...
1.) No Nipples (front or rear) OPEN Emissions applications only (always without Thermactor)
2.) 1-Nipple (up front, w/90 degree elbow), CLOSED Emissions, No-Thermactor (sort of rare)
3.) 2-Nipples (one front, w/90 degree elbow + one straight nipple on rear for Thermactor)
Perhaps others know more about Hi-PO applications, I do not.