Originally Posted by Brian_B
The ford truck 9" is a bolt in from 57-73 into your 56.
The 57 to 72 F-100 rear end is a bolt in ... no cutting or having to narrow it. It is a way better rear end than the 1996 Formula rear end. The only reason I could see for using the Formula rear end is ... IF ... it is a disc brake equipped rear end.
The 9 inch Ford is a lot stronger and a lot easier to work on. I would just install the Ford rear end and then buy a center section with a gear ratio very close to what the Formula has ... if I wanted that gear ratio. A lot of the Formulas had a 3.42 gear ratio. Ford has a 3.50
The Formula rear has a lot of stuff that would have to be cut off ... new axle pads welded on ... and I believe they are too wide.
A 57 to 72 F-100 rear end is just over 61 inches wide ... measured this way
A mid 70's Firebird/Camaro rear end is about 2 inches wider than the 57-72 F-100 rear so I know the 96 is too wide.
Moser Engineering can shorten your housing ( $110 ) and shorten axles. Same price
But not all axles can be shortened ...
Moser has a web site ... below