from the little bits of info I'm come to know, here are somethings you might want to consider.
Factory injectors and fuel pumps run out of juice around 210-230rwkw so you can have 4 truck sized turbos hanging off the side and you still won't make anymore than 230rwkw.
I'm thinking the exhaust manifold will have to be replaced with custom ones to fit the two two turbos.
New twin dump pipes will have to be either purchased or replaced.
Twin air flow meter
Aftermarket engine management
Inside the engine, I've heard you will have to change the pistons, something to do with the change in compression. Will also have to change the gasket as wel.
Pretty sure I'm missing a few things
Injectors - $900
Fuel pump- $200
twin afm - $500
exhaust manifold - beats me, anywhere between $400-$1000 I guess
Power FC- $1500
New pistons, conrod etc etc - dunno a few grand or
gasket - don't have a clue
a tune - $500
Dump pipes - $x00
well, thats as much as I know.