Here, read this So You Want A 3.8 Turbo Z Car
Personaly, I would build up a small block Chevy on the side, while you're still driving your car. Read up and build the engine right for turbocharging. When the time comes, swap engines, then sell the stock engine.
Don't forget, with more power, you will need to upgrade things like: brakes, chassis, differential, halfshafts, stub axles, transmission, fuel system, ect. Twin Turbo 350 V-8 sounds cool, but it's not cheap.
!M!