Just a thought could OGB mean Opperman Great Britian.

http://www.gracesguide.co.uk/S._E._Opperman

1939 Opperman Ltd. (S. E.), North Circular Road, Stonebridge Park, London, N.W.10. has been engaged for many years cutting gears, making beaching gear, bomb-winches, anchor-winches, motor flap-control gearboxes, and main flap-actuation gear for the Aircraft Industry. The latest product of the firm was the 60 h.p. Walter Mikron motor, built under licence, for which the selling agents were Chrislea Aircraft Ltd., of Heston Airport.