Engine rebuild.
See
www.lcengineering.com
Not sure if it's wise to turbo charge a standard 22R.
Much better to base it on the 22R-T.
This is already turbocharged (although very mild in stock form) so it has the extra webbing to make it strong.
Any 81-85 Cellica will do for a donor car.
Doesn't have to be a GT, the parts all interchange between the ST, GT and GT-S.
And truth be told, the main differences are in the trim and accessories.
Many parts interchange with the the Supra too (eg seats, dash, doors but not much in front of the doors).
Personally, it sounds like it's too far gone to be worth fixing.
Cheaper and easier just to buy another in better condition.
- Stepho