I believe our site sponsor provides some info about ratios for this year under axle codes.

http://www.americanclassic.com/paint.htm?p1=axles

I inquired about a 12 bolt rear end for sale recently and was told there was a sequence of HQ 1215 W on the axle. I interpreted this as a 1966 3.73 ratio built on December 15 at Warren, MI if I recall correctly.

Another vendor provides a list of RPO codes for rear ends on their site. The RPO numbers may be found on a sticker in your glove box?

http://www.drivetrain.com/gm8.875trk.html
http://www.drivetrain.com/GMtrkratio_posidata.html

Hope this helps.

Last edited by randy luton; 11/10/2007 7:57 PM.
"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson