I'm on lunch break teaching a framebuilding class so this has to be quick. SD5782 is a buddy that has some mutual interests in old Schwinn Super Sports. I don't have time to properly explain how to better check alignment than methods often advocated in the general C & V discussion forums. I learned at Ellis Briggs 50 years ago and the latest owner Paul Gibson took my class many years ago so I'm pretty sure what Paul said in his video would agree with my philosophies (even though I haven't had a chance to look at it yet).

British made frames were often poorly made and having seat stays not equal in length is not surprising. One thing that can be done (after properly aligning everything else) is the bend the bottom of the dropout down just a little. In other words widening the slot. When the wheel axle rests on the bottom of the front of the slot, it is possible to get the wheel closer to center after bending it a bit. I think regular steel frame usurers would be shocked at how poorly many frames are out of alignment from poor building methods. .