If anybody wants to have a go themself, this is what I used and did:
I used (for the feed to the i/c):
3x 90 degree 2" bends
some 2" pipe, I cut lots of bits of pipe at about 15 degrees at one end, so they could be rotated and welded to form curves in the pipe to get round obstacles. It took lots of trial and error and going back and forward to work with bits of pipe in my bag (isn't night shift great!) to get it right.
Once it was welded, I buffed it down with a flap wheel and gave it a polish up. There's actually about 12 joins in it. The turbo outlet was made from a bit of 10mm stainless plate, cut out roughly with a plasma cutter then attacked with a grinder to get the shape.
The outlet from the i/c is about 6" of 2.5" pipe welded onto a stub flange connector. The other end of the connector is welded onto a 2" bsp elbow that's welded onto 3' of 2.5" pipe that goes straight to the plenum.
I had to cut a bit out of the body where the pipe goes up to the plenum, I used a 3" holesaw, welded the panels back together where they'd been cut and gave it a coat of paint.
On the i/c I cut the ends off (obviously) drilled a 2" hole in one side and a 2.5" in the other and stuck the pipe in with the good old titanium putty, it probably could have been brazed, but I can't do that at work. I cut out 2x 2.5" bits of plate and stuck them over the ends where the old inlet and outlet had been.
I used stainless steel for everything and even if I'd paid for it it wouldn't have been too expensive:
2" bends are about £5 each
2" pipe is about £4 a metre
2.5" pipe is about £5 a metre
I know the coupling I used for connecting the i/c outlet pipe is dear, but a silicon bend would be a lot better (i just used the coupling because it was lying around, and I'm a tight git).
I welded a stub into the pipe near the plenum to attach the dump valve to (1" bsp coupling I think) and did another pipe without the stub so I could run without a dump valve if I wanted, then I realised I'd have to take the bumper off to change it, so it'll sit in the garage doing nothing now
I also moved the air filter and for that I just cut a bit out of the pipe between the filter and the turbo and plastic welded it together again.
If anybody wants any more info, feel free to get in touch.