The twin turbo supra engine, the 2JZ-GTE, was first used in the JZS147 Aristo (MK1 GS300) so yes you would be able to do a transplant. I'm not sure what gearbox the GS300 has in it but the Aristo has a A340E, they all use the same model number MK3 Supra, MK4 Supra, GS, Aristo, Soarer (I think) and more I imagine. But are slightly different depending on what engine they are bolted to, think the splines are different.