No offense, but with these questions you seem very ill prepared.
Converting your car to AWD is something that is based in fantasy land. I am not saying it can't be done... just that the time, money, R&D to make it work would not be worth it. It would be cheaper to swap your car, and buy a WRX imo.
I won't even get into the transmissions. Do some searching. You won't be using the AWD trans unless you heavily modify it. Not worth it IMO. There is a writeup on using an RB bell on a Z32 trans. Read it.
I am 99% sure there is no RWD 6 speed, or AWD 6 speed for that matter.
Evan