just a little input (hey, i couldnt not help out!)

you ask if the 20v manifold would be a straigiht fit, i believe it would be however if you are wanting to go bigger turbo and new exhaust route then i would strongly advise a custom header be made to take whatever turbo you choose to go for. i know my friends garage makes custom stainless headers to the customers spec for about the £250 region, this is for N/A cars tho, i cant imagine a turbo manifold being much more tho.

i notice you are in north yorkshire, maybe tyneside is to far but i could certainly put you in touch with my friend if you were interested, he specialises in getting insane amounts of power out of otherwise pretty tame engines, example is his show car, a 1.6l corsa running throttle bodies and a completely rebuilt head and putting out 190bhp N/A, not to shabby eh