Are you interested in staying original, or would a work-around be acceptable? It's fairly simple to rig a bracket with a micro-switch mounted on it to operate the backup lights.

There's a huge selection of them on Ebay- - - -search "micro switch". I like to use the full-sized 15 amp switch with a roller on the actuator arm. Bracket it so the shift linkage moves the arm when it goes to the reverse position. A piece of steel flat stock held to the steering column with a radiator hose clamp or two works nicely!
Jerry



"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!