8.75

HemiSSDart said
52-5/8"...Don't know where they get 51.4"?

I just measured the 3 OEM A body 8 3/4 housings I have.

Outer housing flange to outer housing flange is as hemiSSdart stated 52 5/8"

These two sites seem to have good info.
Moparts on the Web - Main Index

And

Chrysler 8-3/4" Axle Guide