I think they are Flowmaster 40 Series Delta, 2-1/2″ openings. The address printed below took me right to the page for 1965 Mustang exhausts. Form there I’m sure you can find something in the size and sound you want.

This site is for Auto Parts Warehouse. I don’t know where they are located. Their site seems to be pretty extensive.

http://www.autopartswarehouse.com/perfo … &year=1965