He will want a GTR box
You will want GTR brakes and driveline, GTS4 stuff is weaker, get under and measure! Best way to check.
You could get a series 2 Stagea(so a NEO motor, which has GTR rods standard), try and find a manual half cut. But personally i think the cheapest option would be to grab the series 1 stagea motor(similar to the series 2 R33 but rumored to be different cams) and sort out a GTR box, then replace driveline parts as you break them