Maybe didn't post this here yet? '71 Raleigh/Carlton Professional Track, bought as a frameset. With 700x28 Vittoria Corsa tires, actual width around 26mm, clearance at the chainstays and under the fork crown were _very_ tight. With 650b GB Cypres, actual width around 32mm, clearance at the stays is reasonable, 4mm/side, and under the fork is clear as a bell. BB is on the high side, so the lower overall height hasn't been a problem. Getting the long-reach Campy front caliper to reach the rims was a chore, might end up replacing it with something just a smidge longer.
With only a front brake, and Jersey traffic, I went with a modern aero lever plus 'cross levers. Recently added a tandem dummy right-hand brake lever stub, no photos with that yet.
Before, 700c:
After, 650b:
