I'll bet you have a transistional Pre/Model marked 39. S&W was using up parts. I own one as new with box, and papers. Mine had a long beaver tail frame, but all the other accents were Pre 39, Short safety, no cut stocks ,and a Pre 39 magazine. I had it lettered by Jinks. They are more rare than the Pre 39. If it's alloy, you have a pre 39 frame. Looks like the rest is pretty much a Model 39.