Comparison Scans courtesy Kanstul USA

Note the symphonic 4s-1-28 in blue. The 4s ("for symphony") series are the deepest/largest Al Cass standard trumpet mouthpieces made by Al Cass. 

The 3 series. 3x1 is deepest (red), The 3x7 shallowest (amythest). Note there is no 3x6 shown, Note the gap between 3x5 and 3x7.

Scan of 2 series rim & cup shape, only variations would be throat size 24-28 and backbore. (A was the only backbore option).