Low volume/ used import vehicles need to satisfy the criteria of being a performance car or a vehicle of special use (ie disabled access, campervan or truck). The non turbos were under the power to weight ratio set.
The auto will bolt up (same blocks) but you will need to change looms as the turbos have additional wiring for wastegate control etc, and coils are in a different place.
Fuel pump will also need to be changed.
I'd look at putting the VR4 brakes on too as the ST-R ones are quite small.
Not sure what else you will need but I'd take it easy on the box as the transfer case and gearbox for the ST-R are smaller IIRC.
I'd try to pick up an auto and transfer case for cheap. The open diff at the rear is fine to use (some of us are switching to opens and putting LSD centres in them).
The autos can be picked up for about $150ish from memory from Zebra or Pick a Part, and transfer case is an extra $80 or so.
However if you can find a complete manual VR4, you can get a full manual conversion from Zebra for $300 or so from memory. They have a set price for everything you need for a conversion.