3OTT Saginaw converted to Indy floor shifter - How to get backup lights working?

[Yamariv]

I've been working on cleaning up leaks in my Saginaw Tranny lately and I'm wondering what would be the easiest way to get my reverse lights working again?

I understand that the lights were originally connected on the column to a switch, connected to light and dark green wires. In my research, looks like the 4 speed tranny's had a switch right on the transmission that gets bumped closed when the reverse gear is selected. Is that switch possible to add to a Saginaw 3 speed? I've attached a picture also, there an opening that's plugged up that I've circled, anyone know what that opening is for?

Thx!