Stop in for a cup of coffee

GeorgeH said
42 rh is smaller 904 based, 46 rh 727. 42re and 46re are the electronic units. I'm not sure on the year break for rh/re but i think it's around 96. The 42 fits with less floor hackery.

Yes, you need to get the RH tranny unless you plan to add electronic shift control.