If this rear axle is a 9", and I'm looking for a 5x4.5 bolt pattern, this looks like a pretty good fit yes?? (according to FTE rear axle swaps webpage)

1972 Ford Mustang Boss 351- Parting Out-Cheap


1948 through 1960 Ford F-1 and F-100 Rear Axle (differential) Swaps .: Articles

 

I could be wrong, but my recollection for the axle width of a 71-73 Mustang is 58", not 61. I woould recommend verifying any information found online. Contrary to popular belief, just because it's on the internet, it doesn't always mean it's true. LOL

All that said, that Boss is worth more complete than the sum of it's parts. It's a shame that one is being parted.

 

That's indeed one rare Boss, since there were none made after '71!

 

According to the research done on
https://www.ford-trucks.com/article/...ial_Swaps.html

Just Right

57-72 F-100 measures 61" (5 X 5 " bolt pattern)
71-73 Mustang- measures 60 - 61" (Not all are 9", some are 8") (5 X 4 " bolt pattern)
67-73 Torino, Ranchero, Fairlane- 9" 59"to 61"
67 Cougar- 60 inches
89-01 - Ford Explorer 8.8" 59" 59 " (5 X 4 "car" bolt pattern)
89 Lincoln Mark VII- (per F100Connection.com) (width unknown)

 

I'll have to go measure it and check it out in person, but I wanted some reassurance before I make the drive....