Sure would have been easier if you had mentioned that up front.
The application I gave was for a 72 C30 1-ton truck or a P30 1-ton step van. Since you have a 12 bolt (now stated) I spent some time looking for you. GM parts wiki is showing RAC as a 78 C10 12-bolt open 2.76 axle. There very well might be others.
Here are some links if you want to look around. Sorry, my connection is not fast enough nor do I have the time for most non-67-72 requests that are outside stock applications.
http://www.gmpartswiki.com/getpage?pageid=60434
http://www.gmpartswiki.com/getpage?pageid=60426