IMO it would by cheaper and easier to convert it to a 18rg than to convert a 3t-gte motor to NA, as for power lost not sure on figures but standard 3tgte against 18rg a very considerable power difference.
Plenty of info on engine swaps on the forum if you wanted to go for another variation of NA motors.
Might even be cheaper to look for another Celica with a NA engine.
I hope that helps
Aaron
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