That's good news. I really hope 250bhp is achievable with just a rebuilt turbo and tune.
I am currently speaking to TDI Turbos, I just need to find a tuning company. I am in Medway, Kent so if someone could recommend a company in the south east.
To increase an turbo diesel engine's performance with 30% without heavy modifications are relatively risk free. When you are looking at 70% you need to look at modifying the whole system. A chain is only as strong as its weakest link. At 250hp you should probably modify the clutch to handle that kind of torque. You will need a bigger exhaust too.