After some further research, I have found this to be 10000000% true - they are exactly the same, the difference is in the crank, deck height, and pistons between the 4G64 and 4G63.
Regarding the JE Pistons, what size over bore did you get and were they available off the shelf or custom made? I am looking for a set as well as forged rods.
As for power handling, I would think that 350hp (engine) would be easily attained before the turbo hit 20psi
