Theres a couple junked SC 300 and 400 autos at the local yard, does anyone know if these are interchangeable to the rear of the 5 speed na supra? I know the TT auto is, but what about the SC's? sick of the 4.27 gearing on the highway, its rediculous

 

Yes, both Supra n/a differentials and the Supra TT Auto differentials are cross-compatible with all SC differentials. You may have to swap the companion flange to mate to the driveshaft, but the subframe mounts and the axles will bolt up for certain.