Hy if you measure 68 it is an Britisch Threat BSC. If you like to replace it there are many from Shimano or Campagnolo available. You may install also the Shimano Oktalink Bottom Bracket with Ultegra Crankset. (I did it on my 83 puch) For upgreading the Brakes is the best if you use new Shimano or Campa Parts, they realy have an better performance than the old Weinmanns and will fit without problems