The distance between dropouts is 110-115mm. What would the bike be likely to have been set up with originally if not a freewheel? Single speed? Hub gears?
Anyway, it seems I have an early Cyclo Benelux derailleur and shifter spare!
Almost certainly one of the following three:
1. Sturmey Archer hub gear - underrated and aesthetically pleasing on a 40s/50s bicycle.
2. Three speed freewheel and derailleur (my Father had this set up on his tour in France in 1953).
3. Double sided hub with a fixed one side, freewheel the other (or even two fixed or two freewheels).
The Sturmey hub would be my period choice as early derailleurs weren't great when new.
R.O Harrison was trained by Maurice Selbach, and my Grandfather knew Maurice, who was killed whilst riding to work in, I believe, 1935.
Co-founder of a V-CC section, member South Eastern Road Club and owner of - 2005 Bianchi Reparto Corse (modern), 1985 Raleigh SBDU Pro Super, 1984 Raleigh LU Corsa, 1980 Allin Stan Butler Special, 1978 Ron Cooper, 2 x very early Roberts (late 60s/early 70s), 1975 Bill Philbrook tourer, 1966 Raleigh Superbe Roadster, 1964 Allin Stan Butler Special Belgique, 1951 Hobbs of Barbican S/C, 1950 Hobbs of Barbican S/C, 1947 Hetchins Super Special, 1908 Centaur Featherweight. 1988 Specialized Stumpjumper.