if you look into ur engine bay, 1 of ur turbo is near the radiator and the other is near the bulkhead (below windscreen). so imagine how to plumb 6 cylinders from different banks and to make the primary pipings the same length, where to put the single turbo etc etc...(not like skyline or supra, even though 6cylinder but its inline and can do piping similar to inline4 evo vr4 etc)
im sure the lag will be more than the original TT setup.
look around ur perdana twin turbo engine bay, from the top, from underneath, look how the exhaust go out from the engine, where the turbo is, then you'll understand...