need some help

i just recently bought a beautiful 1986 bmw L7 runs great but i need a shift converter for it. the car goes anywere in reverse but wont go forward i was told i needed the shift converter to fix it and then i was good to go. also this bmw is the candian version so i was told that instead of having to drop the trans. it was located in the back and i get to it by droping the real axle. does anybody know anything about this part and were to find it. thanks in advance