1937 16H speedometer issues

I'm a little confused re: my 1937 16H speedo. I have a tank top instrument panel - the speedo bezel is 3.25ins diameter but the hole is 3.17ins. So the instrument sits up by about 3/16 ins. Too much for any sort of gasket. So the speedo I'm guessing that it must be a replacement. It only has 2700 miles on it. But it seems odd - maybe the bezel is all that is incorrect?

Stamped underneath it has 'S276-10-36' on a plates screwed on. Maybe PO moved the plate?

One question that someone is more likely to know the answer - if I look up at the bottom should the shaft turn clockwise or anticlockwise? If I test it on a slow drill or even twiddle it between my fingers, will I do some damage if I turn it the wrong way? Its a Smiths/ Jaeger chronometric of course.

Thanks in advance

David Cooper