Yes, corona gear box can fit 3sgte,but make sure is the 2.0L 3S-FE version,
not the 1.6L version . Modify 3S just like modifying other turbo car , change a
bigger turbo, bigger injector, bigger fuel pump , better ECU or stand alone ECU,
racing clutch , waste gate , racing bearing ,without changing internal part it is good for 350whp,
I saw a 3SGTE boosted to 400whp with NOS , stock internal ! No problem at all.
But you looking for more serious power , then change to forge piston,conrod etc.
What kind of mod you are looking for ?