OK I searched voltage regulator - nothing. I have found that Stevens NY made a lot of special Ford tools for Model T's. Alloy Artifacts says Stevens merged with Walden-Worcester in 1926 so the tool can't be much newer than the Model T era.
I've tried a number of different search terms including tool, adjuster, Ford, Model T, auto, voltage regulator, magneto, contact breaker, ignition, etc, etc, with and without Stevens or Stevens New York. Lots of Stevens tools - mostly Model T - but nothing at all like this tool.
I'll try to post a photo on some Ford and T forums.
Al.