Drill/Tap SM420 for reverse light switch

Does anyone on here know what location I need to drill and tap on the SM420 to install a reverse light switch? Both my SM420's are pre-67, and thus not equipped with the switch.

TX requires reverse lights on a '70 vehicle, and as I understand won't accept a manual switch to turn them on and off when shifted into reverse, as the tech article on this site suggests.

I figure I can disassemble the shifter setup on my spare and find out what I need to do, but I was wondering if anyone knew the details. I'd rather not ship the parts off to Novak to have them do it if I can avoid it... but that may be the best option.