Check the rear cradle mount locations (four big ass bolts) of the gt and gts. If they are the same then switch the entire cradly assembly AND drive shafts. I think one of them has two piece shaft and the other has a one piece shaft but they should switch perfectly.
if you want to go really low without the camber this is definatly the easeist way. Probably better for drag racing too, but I don't know if the rear end would be any stronger, hard to say. Definatly go with celica rear if you do it, no point in messing with custom work to put a mk1 rear in. If your going to do all that put something beefier in like a ford or mk3 rear (yes, much more work).
Live-axle Celicas have a different floorpan to IRS Celicas, so putting a live axle in a Supra won't be easy to do. Personally I can't see the point though; live axle is only good for the drags, and a Supra isn't meant to be a drag car. In every other respect a live axle will be a backwards step.
WHY WHY WHY????? Buy a F-ing Mustang if you want to drag race!!! The celica rear end is a 6.7" it will explode the first time you launch it. If you really insist on ruining your car do it the right way and get a ford 9 inch and have custom axle tubes and brackets made.
Jody Sille the person who has the top turbo drag time here on the messageboard has a solid axle. Though I hesitate even to put it on the list because it isnt a Supra. I would probably bump it if there were 10 other people to put on that list.
yes there would have to be some welding if going with a solid axle but ive thought about it for a long time. i like solid axles better than irs. i can get an axle with disc brakes control arms the whole nine yards for $60 at a local pull-apart. my dad owns a repair shop and im a tech at toyota. so getting it put in will not be a problem. as far as going backwards, i dont see why anyone would say that. the mk1 celicasupras i believe had the 7.5 rearend with disc brakes i used to own one. i was planing on swaping the third member out of my mk2. and if later on, im not happy with it then i could swap in a 4-runner 8in axle with a mk3 third member.
the only way for doing a solid axle swap to be really very beneficial for traction would be to engineer a 4 link rear. there is a lot of thought which goes into building a proper drag racing suspension, and you would lose a lot of the nice handling characteristics, etc., that you already have. That said I have a solid axle in my car (MKI) and it handles alright, but the suspension is stock and not really built for draggin'.