Ford Rear Dimensions
                                by Dave_C and the Fordnatics mailing list. 
Here is a list of rear ends that I picked up some time ago on the Fordnatics mailing list.
These measurements are from flange to flange. Subtract 5" for bare housing length.

65-66 Mustang 57.25 inches 
67-70 Mustang 59.25 inches 
71-73 Mustang 61.25 inches 
77-81 Versailles 58.50 inches 
74 Maverick 8" 56.50 inches 
75 Mustang II 8" 57.00 inches 
67-73 Mustang, Torino, Ranchero, Fairlane 9" 59.25 inches to 61.25 inches 
57-59 Ranchero and station wagon rears, 57.25 inches 
66-77 Bronco 9", 58 inches 
77-81 Granada/Versailles, 58 inches 
67-71 Comet, Cougar, Mustang, Fairlane, 59.25 inches 
71-73 Mustang, 61.25 inches 
64 Falcon 58 inches 
67 Cougar 60 inches 
67 Fairlane 63.50 inches (coil springs) 
72 Ford Van 3/4 ton 68 inches 
73-86 65.25 inches 
57-59 Ranchero and station wagon 57.25 iches (narrowest 9" housing) 
66-77 Bronco 58 inches but has 5-on-5 1/2 inch diameter bolt circle 
67-73 Torinos, Rancheros, Fairlanes 59.25 inches or 61.25 inches 
67-71 Comets, Cougars, Fairlanes 59.25 inches 

Where to find the 9" rear axle
67-73 medium and big block Mustangs and Cougars 
66-71 Fairlanes, Torinos, Montegos, Comets, and other Ford intermediates
with big blocks 
57-59 V8 Fords and Mercurys 
77-81 Lincoln Versailles & Trucks 

Type of 9" axle housings
67-73 Mustang/Cougar - light duty, thinnest housing material, small axle
bearings, 28 and 31 splines 
57-68 passenger car and 1/2 ton truck - medium duty, stronger than Mustang
type, 28 and 31 splines 
Ranchero/Torino - heavy duty thick wall housing, 3.25 inch diameter axle
tubes with flat tops 
69-77 Galaxies (coils), Lincolns (coils), and late pickups (leaf)- 3.25
inch diameter all the way to the backing plate, coil housings have upper
control arm mount 

How to recognize 9" housing centers
57 - no dimples, flat center band up the center of the rear cover, bottom
drain plug 
58-59 - two dimples on back of housing, flat center band, some had drain holes 
60-67 - two dimples, flat center band, oil level hole in back cover 
63-77 Lincoln, LTD, Thunderbirds had 9.375 inch centers, housings were cut
away at the gasket surface for ring gear clearance, one curved rib at the front 
top portion of differential. Strong, but no gears.
 
Types of 9" Axles
28 spline axles cannot be shortened and resplined (they're tapered) 
Some can: 69-73 Mustang and Cougars have a straight 28 spline axle.
72 and earlier 31 spline axles have the ability to be shortened 
73 and later 9" (big cars) have a 5-on-5 bolt circle and the axles cannot be
shortened 
67-73 Mustang axles identified by wheel flange: 
oval hole - 28 splines two large holes and counter sunk center - 31 splines