I cut a measuring stick to represent the original axle width inside measure behind the brake dust shield left to right. Took this stick to a junk yard and started checking out cars that had late 60' and early 70's 10 bolt rear ends. The closest I found was a 1970 Oldsmobile rear end 272 gears, came within 3/4" of the original width. Works real well and the width looks stock. Looks good bolted custom driveshaft to a 700r4 & 4.3 v6.
Consistently gives me 22mpg.
http://s150.photobucket.com/user/vickraft/media/024-1.jpg.html?sort=6&o=5

1951 Canadian Chev 1/2-ton Shortbox