Just finished this bike today. Got it a week ago. Needed a polish and put on some new rubber, sensible cog and some fresh tape.
Always wanted a Jack Taylor
Re:
I’m currently using a un55 122mm BB. The axle protrudes 25mm and the chainline on my fixed setup is 2mm off. This is why the axle protrusion is important as you rightly said all BB are the same due to offset.