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!
Good luck at the auction!
- Justin