Vintage Mallory Adj. Proportional RPM Limiter

[GaryC]

Can somebody help me out on something? I have, somewhere packed away, a Mallory unit similar to this one in the provided pic, but the dial bezel isn't red, it's silver with a blueish color banner that has MALLORY at the top of the bezel over the dial knob. Anybody familiar with this piece? I'm pretty sure it's vintage but don't know a lot about it...how old and what model. It is very similar to what's in the pic. From the looks of it it had a rough life. I can't remember where I packed it or I would provide a pic. Anybody have any vintage Mallory parts books to determine what I have? At one time it did work but since I removed it 20 or so years ago I'm not sure. Is it even worth having it looked at? Other info I found on line for part number is #642, 643, and 644 but without a pic IDK.