Just found this - LINKY - might be of use to some here ?
And I was wondering if the forward/backward movement of a car type gear lever would work ?

I can see that kind of design getting out of sync with the actual gear selected at the first missed shift, or when getting into neutral etc.

I thought that, but you could sanity check it with an rpm/wheel speed comparison.

I invented an almost identical PIC based one which is still on my website....

Works fine once you have the microswitches set up correctly....