can u run a 13b engine with a 12a 5 speed.......also what is the difrence in housings from a 13b and a 12a

 

I believe you can run a 12a tranny. I know you can run a 13b tranny with a 12a, so I would assume it's the same bolt up.
If you're asking about rotor housings, I think it's a 10 or 11 mm difference in thickness.

 

Bell housing pattern is the same for all rotaries except the very early ones.

You can run any RX-7 tranny on any RX-7 engine provided you mix and match the correct flywheel/counterweight,clutch and starter for the application you are putting together.There are minor differences in the shifter location and rear mount,and there are substantial strength differences between the N/A tranny and the turbo tranny.