Pretty sure the first celica GT4 (st165) was a turbo gen 1.
The small and large outlet on the back of the gen 3 heads are incorporated into one outlet. The turbo line then comes off the that coolant "manifold".
I have one in the shed if anyone wants a pic.
The double row spigot is easy to find, just measure (from memory it's 36mm OD and 12mm ID) then go to your trusty bearing supplies and spend $45 bucks buying a 16mm wide double row ball race.
Standard one is 9mm wide and under $10. This is what I have used. I had to machine the bell (-8mm front, -2mm rear) and reset the fulcrum ball for the clutch fork. I also had to extend the bearing slide.
These last 2 things were done to push the clutch plate further onto the gearbox input shaft and may not have to
be done on the gen 1 as the flywheel is more of a rwd profile.
Slydar can confirm this though. He has first hand experience with the gen1.