Hi Ross
The R32/R33 transfer box have a much bigger chain inside than the R34 version. Having said that, I haven't heard of an exploded R34 transfer with big HP (up to now). So, I guess you can take either. Have a good look at the For Sale section; there's at least one R32 I know of that's being parted out. You can also try Abbey Motorsport, they may have a transfer box.
Andre.