You could go that route, it'll just cost you a crap load of money, more money than it's worth probably. Just buy the damn RB25DET transmission.
Or the Z32 N/A transmission is the closest thing to the RB25DET transmission, I believe the bell housing is different and a few other minor things. But where the hell are you going to get a RB25DET bell housing?
Output shaft, input shaft, clutch are all the same as the Z32 N/A. Please correct me if I am wrong on any of this.