On my E32 750 from 10/88 parts car I removed all parts and studied that. On left side of the IHKA unit there is a stepper motor, and that is connected with both flaps, left and right side with a bowden cable.
You can access that the same way as you want to get to the blower fan motor.
http://bmwe32.masscom.net/johan/ihka/ihka.html