I know that I need the 3 speed motor, link arm (off the motor) and a bushing(?) to change to a 3 speed. I have the whole linkage setup out of a 3 speed car too though not sure if I need all the linkage but probably be easier just to use that set up.

Correct, all the wiring is the same. I have a non rallye dash, so do I need a non rallye 3 speed ebody specific switch? And if I understand correctly, the non rallye is different then the rallye switch?

I would like to change over to a rally dash at some point as well.