http://www.chevellestuff.com/tech/rear_end_widths.htm
Also, I found this on chevelle.com
* 1964-67 Chevelle rear ends were manufactured by the Chevrolet Gear and Axle Division. The housing measures 56.5 inches from flange to flange, and with the brake drums in place, the total width is 60.5 inches.
I had the stock 10 bolt of my chevelle laying behind the shop for about 6 months, finally I had it hauled away last week or I could of went and measured to be sure.