Hello Everyone!

I need some help to identify this narrowed rear end. I have only pictures of it so I cannot
tell you any cast numbers. The seller who I bought it from doest know too much about it.
As far as he knows this is a GM. But which one?

 

kind of look's like it is in the mid to early 60's but iwould look at it closer and get some casting numbers off of the center section and track it down from there ,might be able to use a hollander manual to track it down .good luick