Welcome to the site, Riley.
As you may know, there were four species of air cleaner housings originally produced for the Ford y-block 2x4 set-ups. Two were used in the late '56 model year and two during the '57 Ford model year.
- the over-the-Ford-parts-counter Power Pack kits released late in the '56 model year that had two different air cleaner housings. One was for '56 passenger car installation, the other for '56 'Birds. -Both of these air cleaner housings, one round, one oval, oriented the Holley 4000 carburetor chokes to face the firewall. The oval housing was intended to fit in the limited space available under the 'Bird hood.
- the round circumference unit supplied on '57 'E' code passenger cars had the carburetor chokes facing front toward the radiator
- the round circumference unit supplied on '57 'E' code 'Birds cars had the carburetor chokes facing rear toward the firewall.
The '57 'E' code air cleaner housings had...
- the domes extending above the top housing 1 inch higher for the 'Bird unit
- the perimeter skirt on the upper housing 1 inch shorter in height for the 'Bird unit
- the paper air cleaner element supplied for the 'Bird unit less tall than the one for the passenger car unit
- the raised lettering 'FRONT' marking on both top housing domes is turned 180 degrees for the 'Bird when compared to the passenger car
- the lower (base) housing is identical for the '57 'Bird and the '57 passenger car application. That housing is turned 180 degrees to properly line-up with the Holley 4000 carburetor air horns depending on whether the chokes face the radiator or the firewall.
NOTE: the top housing of both '57 'E' housings is the same except for the dome heights, what's front and rear for installation of the upper housing on the carbs, and the height of the housing side skirt. Oops! The side skirt for the passenger car air cleaner upper housing also had a curved indentation to give clearance to the oil fill tube that connects to the valley pan.
I'm aware of previously produced aftermarket reproductions of the '56 'Bird Power Pack oval air cleaner housing and the '57 'E' style air cleaner housings. Some of the reproductions I'm told required serious attention to detail to identify them as repros. I've seen one knock-off of the oval unit that some would say was better than an original because of the increased thickness of the sheet metal used. Interestingly, the one I looked at carefully had a late model oval air filter element used instead of utilizing two round elements as original. While the tooling for producing these likely still exists, methinks that production is limited to prevent reducing pricing. I don't know of any current source for any Ford original 2x4 style reproductions.
Hope this info is of some help in your search.
a.k.a. Charlie Brown
near Syracuse, New York