sounds like a cool idea. suits the old school vibe of the car and will be heaps of power.
all the rest of the q's youll have to ask someone who knows rotors.
i think a rack might be a better idea though, more clearence for the ex, its on the drivers side on a rotor remember.
i would say a toyota g'box will be better, than the rx7 boxes ive seen (which are all gen 4 on) as those things need a huge tunnel (like an s2000 box)
you might need to get the bell and then measure, once the engine position is determined... the select whicever w box has the right extension housing.. but usually, its the furtherest back (not including the NA jza80 one) that works the nicest as with a toyota bellhousing on, its about the same length from engine mounting face to shifter as a corolla type t50.