I meant to add, the 57 Ford 9" rear - and a lot of the 8" rears - is 57 1/2" wide.

They work well under the early cars . . . provided you can find one.
You're only gaining 3/4" per side as compared to the accepted standard of 56" wide.

If you should be so lucky, try to find a 57 rear axle from a station wagon or Ranchero.
Many of these - depending on the engine - had 31 spline axles althought the 28 spline axles work well on the street when running an open diff.