Hrmmm.... Not sure if any of the Supra's or the CelicaXX's had the 1G-EU motor. The GA61's had the 1G-GEU. The 1G is a 2.0L motor, you'll need to look at the motor page that is at Matti & Helene's website.
Cool - you've found an imported Supra (aka Celica XX). It would have started its life rolling on the streets of Tokyo or some Japanese city. Aside from a few minor differences, it's basicially pretty similar to the US spec. Supras (I'm assuming you're a yank). Only downside, it that you are looking at a fairly slow (and extremely rare) 2 litre straight six engine. But, the good news is that you can turn it into a very fast twin turbo 2 litre straight six - if you want. I don't know how hard it is to get 1G-GTE's in the US, but if you can - this would make an awesome up-grade. If you're interetsed in going that route, talk to JustCallMeFrank on these boards - he's in the middle of doing this same swap into a 1G XX.
Well, actually I am in New Zealand. So I am not sure how easy I am going to find parts etc. But there was another supra being sold at the same tender, so I might get lucky. Is it possible to put a turbo into this engine? Can it handle it with the right mods? Or I am thinking too high?
Ah, a Kiwi. Cool! Parts for the 1GUE type engines might be a bit tricky. BUT, that 1G-GTE swap would be very easy - these motors are readily available in NZ as are parts. And then you have TWO turbos
Try to find the NZ Supra Club (I don't have time to look up the URL atm). There is a guy on there who has dropped a 1G-GTE into a Celica-Supra XX. You could ask him/them for more local info.
As for the other Supra, you may get lucky and get a 5MGE. From memory, Toyota NZ imported their Supras from Oz in the 1980s (which means crappy single cam 5ME motor). BUT, I'm told that therer were a stack of Celixa XX's and Euro. spec Supras 'grey' imported in the early 1990s - so it could be a 2 cam 5MGE!