W50 5sp Celica box goes really well behind a 6cyl Holden engine, try and get one with the cast iron housing. As for triple SU carbs... pfft.... great if you like spending time tuning them before every drive, I had them on a 186 HR back in the 80's.... best thing I ever did was remove them and fit twin Dellorto's. You'll still have to tune them but no where near as much as SU's.