Here are some catalog pages related to Simplex dropouts that I've collected over the years:

1954 (DisraeliGears website)


1960 (DisraeliGears website)


1964 (source unknown)


1971 (DisraeliGears website)
It seems to me that the dropouts in question are the 932-935 {edit} 880/881 series, and that mudguard eyelets have been removed on the Payan frame (agreed that it looks like a very nice frame) -- I've never seen these dropouts without them, and there seems to be some rust and grinder wheel profiling, but I could be wrong. I have two frames with the 881/881B dropouts, lacking the derailleur hanger, and they're less {edit} not very beefy, about 5 mm thick, even though clearly forged.