This is on my reworked 1920 police with two matching mags one nickel and one blue both have aluminum bottoms. I find it odd that it has the two dots after the number. It was a commercial side plate at one time as it is marked "54" underneath. Magazine safety has been removed and filled in but the notch was not blued to cover. Take down lever is also commercially numbered. Ideas???????????
http://www.cityscape.net/~dgeorge/978.JPG