Wonderful bike! This type of Simplex derailleur and lever is from about 1956-59. So I asume the bike is a bit newer then you would think.
Does it has a framenumber? Mine (a Reynolds 531 Bontekoe Super Sport from about 1960, which I'll show a bit later on, when the retauration will be finished) has a framenumber in the bottom bracket: 414.