B-body 8 3/4 axle for A-body car!

The following "and other great info" can be found at:
http://www.moparts.org/Tech/Archive/axle/21.html


Section 3: Part Numbers and Dimensions of Axles and Housings.



Body line Track Perches Notes

------------ ---------- ----------- -----------------------

A-body, 65-72 55.6 43.0 4" lug bolt circle,

Offered in heavy-duty apps.

B-body, 62-70 59.2 44.0

B-body, 71-72 62.0 47.3

B-body, 71-72 63.4 47.3 station wagon

C-body, 64-72 63.4 47.3

D-body, 64-72 63.4 47.3

E-body, 70-74 60.7 46.0

Also check this one:
http://www.moparts.org/Tech/Archive/axle/16.html