Driveline vibration

Hello,
On my 1974 Hang 10 I have been restoring I finally got it to a condition to drive on the highway. I has a cyclic vibration which is the worst at 45 MPH (bucket seat starts to shake). Putting it on rear jackstands, removing the rear tires, bolting on the brake drums, and then running up and down the speed range no improvement. Swapped driveshaft rotation 180 degrees no improvement. Removed driveshaft and had checked out for balance by a shop and it and U-joints are ok. Started investigating the automatic transmission rear bushing/bearing (as discussed elsewhere on forum) and maybe this is where the problem is. With the driveshaft still removed, I can move the rear output shaft at least 1/32" radially. So my question is, how much play should I have and maybe the rear ball bearing is the problem?

Thanks for your thoughts.
Warren