7.25 Replacement
I finally stumbled on the correct search parameters so I guess I answered my own ?. Hope this helps out somebody else.
http://www.dippy.org/forum2/index.php/topic,189.0.html
Chrysler Corporation Passenger Car Rear Axle Dimensions and Identification: 1962 to 1989
Below is a chart and diagram showing rear axle dimensions for Chrysler, Plymouth, and Dodge passenger cars manufactured from 1962 to 1989. Body lines covered are A-Body, B-Body, C-Body, E-Body, F-Body, J-body, M-body and R-body. Also attached is a chart showing the various types of rear axles used by Chrysler for the same period.
(A) = Flange to Flange.
(B) = Leaf Spring Centerline to Leaf Spring Centerline..
(C) = Centerline of Axle Shaft to Centerline of Rear Universal Joint
Year
 
Axle Type
 
(A)
 
(B)
 
(C)
1963 - 1972
 
7 1/4" A-Body
 
53.200"
 
43.02"
 
10.09"
1973 - 1976
 
7 1/4" A-Body
 
51.400"
 
43.02"
 
10.09"
All
 
7 1/4" F/J/M-Body
 
54.340"
 
44.46"
 
10.09"
1973 - 1976
 
8 1/4" A-Body
 
51.400"
 
43.02"
 
11.69"
All
 
8 1/4" B/R-Body
 
57.800"
 
47.30"
 
11.69"
All
 
8 1/4" C-Body
 
59.200"
 
47.30"
 
11.69"
All
 
8 1/4" F/J/M-Body
 
54.340"
 
44.46"
 
11.69"
All
 
8 3/4" A-Body
 
51.400"
 
43.00"
 
12.35"
1962 - 1970
 
8 3/4" B-Body
 
55.000"
 
44.00"
 
12.35"
1971 - 1974
 
8 3/4" B-Body
 
57.800"
 
47.30"
 
12.35"
1971 - 1974
 
8 3/4" B-Body S.W.
 
59.200"
 
47.30"
 
12.35"
All
 
8 3/4" E-Body
 
56.500"
 
46.00"
 
12.35"
All
 
9 1/4" B/R-Body
 
57.800"
 
47.30"
 
11.69"
All
 
9 1/4" C-Body
 
59.200"
 
47.30"
 
11.69"
1966 - 1970
 
9 3/4" B-Body
 
54.936"
 
44.00"
 
13.47"
All
 
9 3/4" E-Body
 
56.500"
 
46.00"
 
13.47"