not 51.40 no way no how. That's from the bogus POS chart that got published years ago.
A stock a body rear from wheel mount/mount surfaces is 57 1/8"
The housing itself is 52 5/8.
That ford rear is about 1" total wider than a 68-70 B body, 60 1/8", which gets used in A body cars quite a bit. They do need a bunch of neg offset as mentioned. Like a 8" wheel with 5.5" of backspace