Friends, here's a good used Lucas RTS-1 overdrive transmission interrupter switch that's been bench tested. I used a 12 volt power source hooped up to a test light to show the functionality of the switch, albeit, the range needed to active this switch is slight, but it does work! ( See pics) .

Austin Healey 3000 Lucas Overdrive Interrupter Switch Jaguar MK IX & XK140 Too!.