I'm going agree with Stucki's reply as being the most plausible. Had the frame been from a Navy with a stock lug and grip safety it would have been a long frame. This frame is short to fit the short 1915 receiver. I agree it's most likely Swiss modified with the grip safety added. The non-military Swiss barrel doesn't have to be proofed.
I'd like to see beneath the safety lever to see if it is now an up-safety with the lower area marked or polished.
Jack
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