PTO Shaft difference on a early and late A.

Where the PTO shaft links up in the diffy, how does the coupler differ from an early to a late A.

It doesn't. Super A was different.

OK how does the coupler in a Super A differ from the A ?

The A engages with 2 drive lugs. The Super A with something more like a spline with 10 or 12 teeth. They use correspondingly different transmission main shafts to match the sleeve on the PTO. The difference can be seen in the parts catalog illustrations, but not seen that clearly.