My mate still had the original crank tool - 16mm!
I remove the Zeus BB and tried a Shimano cartridge in there but the drive side just fell in, tried the Zeus again and it fitted. I cleaned it up and it's stamped with an 'O' for oversize I presume. So the Zeus chainset will be used in the build
For the colours, we've decided on school railings green/BRG with tan saddle and bar tape
Sounds like the threads in the bottom bracket were damaged at some time and an oversize cup was fitted ( I used to work in a bike shop and we did it quite often )
good luck with this, had one of these when I first joined a club as a boy. the brake callipers and rear mech look original, it's a long time since i've seen Reynolds 501