[STAR]

it has the hole for the 1920 slide mounted safety, but the side of the slide is not milled for the safety movement - possibly an unfinished piece?

Bob please note that te hole is not for the safety, it's for the screw adjustable rear sight. The slide is not for a 1920.

That only leaves us the 1921 or 1922 models, but based on the "T" shaped extractor, most probably is from a 1921, as the production of the 1922 soon deleted that type of extractor to mount the regular one.