It is interesting to me that it seems to have the derailleur stop and, apparently, a threaded hole in the hanger. Did Simplex ever do that? Maybe so. But the 71 and later Simplex dropouts built for Simplex derailleurs certainly had no stop notch. But then, I know very little about these.

Is it your size? Might be a good candidate for a refinish. They're nice riding frames.