Gear selector clearance to casing

[Tinker]

Hi has anyone got a gear selector casing off an engine and can have a look at how much clearance there is around the gear selector near the neutral switch. I am thinking of fitting a gear indicator( not because I need one but my Speedo has the option ) I was thinking of glueing a ring (with a magnet) on the outside of the plate which operates the neutral switch, and a ring of reed switches outside of that. But it would be nice to know if there is clearance to the casing of maybe 3mm or more and room around the plate. Thanks if anybody could have a look and see if this idea is possible or daft