Center of Srping to center of spring
I got this info from the following web site:
hope its helpful
http://www.autohobbydigest.com/8_75.html
Body line Track Perches Notes
A-body, 65-72 55.6 43.0 4" lug bolt circle
B-body, 62-70 59.2 44.0
B-body, 71-72 62.0 47.3
B-body station wagon, 71-72 63.4 47.3
C-body, 64-72 63.4 47.3
D-body, 64-72 63.4 47.3
E-body, 70-74 60.7 46.0