I know it's here somewhere - just can't find it - what is the width on a 64-67 rearend I know it's 1" shorter than 68-72 - but what are the dimensions - thanks

I believe it's 54 1/2" backing plate to backing plate. 68-72 is 55 1/2".

Here is a link to a site that list them by wheel mounting surface.

www.carnut.com/specs/rear.html

64-67 60" accross the wheel mounting surface and 62" for 68-77

Got this info from http://www.chevellestuff.com/index.htm
Click on a year,
then chevelle,
then rear axle codes.

Info is at bottom of page...

* 1964-67 Chevelle rear ends were manufactured by the Chevrolet Gear and Axle Division. The housing measures 53.25 inches from backing plate to backing plate and with the brake drums in place, the total width is 60.00 inches.

* 1968-72 Chevelle rear end housings measure 58.5 inches from flange to flange, and with the brake drums in place, the total width is 62.5 inches. (Note: Other sources put the total width at 61.125" to 61.25".) The 10 bolt Chevelle rear end has the 8.2" ring gear from 1964 to 1972. It wasn't until late 1972 that the 10 bolt 8.5" ring gear was used in Chevelles.
Rear spring mounting pads differed in that 1964-66 rear ends used a flat pad with a hole drilled in the center while 1968-72 rear ends have circular spring mounting pads, which are 3/4" higher that the early flat pad.
1967 was a transition year in that A-cars might have a 1964-66 style rear end, a 1968-72 rear end (which is wider, and commonly available), or a "hybrid" rear end, which will have the 58.5" width, but with the early spring mounting pad and trailing arm brackets. (Note: For what it's worth, ALL 67 rear ends I've ever seen were the narrow variety and used the spring cup like 68-72 but were narrower like the 64-66.)

60 inches over all width.