one good candidate for a gear block for the bike would be a T.D. Cross. they came on many British machines at this time.
VeloBase.com - Component: TDC (Thomas D. Cross) Continental
they require a unique remover. see item nr. 402 here:
http://sheldonbrown.com/var/pages/var0028.html
Last edited by juvela; 10-26-14 at 11:17 AM.
Reason: add information