The air cooled Fordomatic is actually very similar to the later FMX trannys and many internal parts fit. You're right, it is a 3 speed, lots of people think it's only a 2 speed because of the shift indicator only showing 2 speeds. I see no reason why most 3 speed auto shifters wouldn't work, they just won't shift into the first gear position on the shifter. Are you planning to mount it to the floor or onto the trans? Old Pinto and Mustang II floor mount shifters are easy to mount too. If you are doing tranny mount, a shifter to fit an FMX tranny should bolt onto your Fordomatic. The FMX was used in the 60's and 70's.