If I recall, Jon Haas was working on such a thing a couple of years ago. I think he was using six, or more, proximity sensors to determine which gear the shifter was in.
You also might want to talk to Scott Bell.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.