Slumlord. I agree and disagree with you.

'57 'Bird rims and '57 wagon rims appear to be identical in as mounted position without a wheel cover or dog dish on them.
Both the 'Bird and the wagon wheel rims have:
- 14 inch size tires...
- a center hole opening of 2 9/16, almost 2 5/8 inch diameter...
- 5 lug nut openings...
- 5 flat faced ‘spokes’ between the 5 lug nut openings...
- the letters FoMoCo with a surrounding ellipse stamped into the flat 'spoke' surface adjacent to a lug nut opening...
- the letters K-H stamped on yet another of the above mentioned 5 flat ‘spokes’...
- 3 ‘lugs’ that could be used to secure hub caps (not wheel covers) if used...
- no vent slots where the center wheel mounting plate fits into the inside perimeter of the wheel rim...
DIFFERENCES:
- '57 'Bird wheel rims measure 5 inches between where the tire beads seal...
- '57 wagon wheel rims measure 5 1/2 inches between where the tire beads seal...
- ALL '57 'Bird wheel rims have the center mounting plates spot welded to the perimeter rim.
- Many, perhaps most '57 wagon rims have the center mounting plates riveted to the perimeter wheel rim. –look for three button head rivet heads on the backside of each of the four center plate mounting ‘tabs’
- I'm told that later '57 wagon wheel rims and perhaps '58 wagon wheel rims have the center plates spot welded to the perimeter rim, also.
IMPORTANT:
* '57 wagon wheel rims mounted on the front wheel hubs need a spacer so that there is not interference between the wheel rim and the upper ball joints as you experience road suspension movement. My memory is fussy on this, but I think I've hear a 1/4 inch or 5/16 inch spacer plate will provide the needed clearance.
* IF you are using skirts on your '57 'Bird rear wheel openings . . .
- tire sidewalls mounted on '57 wagon 5 1/2 inch wheel rims with no spacers used will clear the wheel opening skirts unless you participate in elevated speed, James Bond-type road course cornering activities
- tires sidewalls mounted on '57 wagon 5 1/2 inch wheel rims will JUST clear the wheel opening skirts . . .
* IF you're running a tire size equivalent to the '57 factory size, but in metric. Fuzzy again, 205-75(?)-14. Somebody doing this now should be able to help here.
* IF the '57 'Bird body was properly located (centered) on the frame when someone did their body-off restoration.
Hope this helps someone!
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York