Mirage frames from the early and mid-1970s use stamped road dropouts. These dropouts do not have an integral derailleur hanger, however the axle slot opening faces frorward unlike track dropouts where the axle slot opening faces backwards. They require derailleurs with a built-in claw adapter. Frankly, I don't ever recall seeing a Mirage with a Simplex derailleurs. Typically, they were Huret Allvit equipped until circa 1974 when they switched to SunTour VGT for the remainder of the 1970s.
As for the spacing, it can vary, depending on the hubs. Many French hubs were actually 122mm or 124mm over the locknuts.