ring gear id help
 

We just went to replace the ring and pinion in my 67 gto and found out it is a 12-bolt housing and it has a 10-bolt ring and carrier. Surprise! So the new gears I have will be reeturned to Summit, but we are trying to find out what to order. The numbers on the ring gear that came out of it are:
13A40 GM HY 236.
Can someone run these and tell me what it is? I have searched the forums and didn't get any answers so please help. I know someone can help.
Thank you!
Bear Lake Rodder

These are considered 10-Bolt rears, Olds & Buick also had this oddball rear. There are very few parts available for these.

Source: Car Craft Magazine - August 1984
Not included in the chart above is the heavy-duty 10-bolt towing package offered by Oldsmobile, which actually has a 10-bolt gear assembly installed in a 12-bolt housing. The ring gear on this setup measures 8.3".
From this link>> http://www.oldsmobility.com/old/10bolt-tech.htm

May try searching for Pontiac 12-bolt or 10-bolt for more Info.

I also read these weren't installed in Goats untill 1970.

Got it figured out
 

Thanks for the help; finally figured it out with your help. Richmond is the only one making a gear for this; going from 3:08 to a 3:42 and paying twice as much for the gear. Love hotrodding!!
Bear Lake Rodder