The switch for the 69 does have three prongs.
So far I have tried four switches and each has had a problem.
#1 was obtained by my repair shop from NAPA. It wouldn't turn on the back-up lights.
#2 was obtained by me from Classic Industries. It would turn on the back-up lights but I would often have to run through the gears several times to get it to start.
#3 was obtained by the repair shop. I don't know the source. It was back to reliably starting the car but no back-up lights.
#4 was a NOS switch I got from Hilltop. It was expensive but seemed to work at both starting the car and turning on the back-up lights. However it is now leaking.
Not sure if I should get another expensive NOS part that might be 50 years old or try another source for a cheaper, non-NOS part that might not work.