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Yes, I see what you mean. The thing is my Simplex Tour De France rear changer is marked for a 1/8" chain, so I assume it is set up and spaced for such, although of course some 50's style bodging could be in order to get it working with a 3/32"....
jeff80-
I think a narrower chain will work, the chain doesn't engage with the smooth pulley wheels, so it shouldn't bind on those, the pulley plates will be a little further apart than a 3/32 RD but it'll probably work. It probably wouldn't the other way around.
I have a 4 speed Simplex 51 (model after TdF) - but that is marked 2.38 -so not a 1/8" chain - but I think they still made them in both sizes.
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I wonder whether a mech intended for 4 speed 1/8th would work on a 5 speed 3/32" block - the width of the blocks must be similar, and since 5 speed blocks are still pretty common this might solve a problem.
absurdbird
clubman
If you look at some mid 50s catalogues and search for 8 speed bicycles those rod actuated front changers normally used 46/49 3/32" chain rings combined with a 4-speed rear (which would have been 3/32" as well). For example the 1955 Dawes Emblem 8 specifically mentions a 3/32" chain is fitted! Same for the 1956 Lenton Grand Prix, also an 8-speed with 3/32" chain.
I would be tempted to use a 3/32" freewheel, maybe even a 5-speed.