How much money do you want to spend?
I heard that putting the turbo & intercooler from the 2.8HS motor in a 200Tdi made a tremendous change. It would probably do the same for the 300Tdi. Try contacting someone who imports the 2.8HS as a replacement motor for Land Rovers and see if they can get you a turbo & intercooler. Anthony from British 4Wdrives (03 9729 9943) imports them and has one fitted to a 200Tdi Lightweight.
Other options would be the LPG / Diesel conversion. I sent the company a query a couple of weeks ago and have yet to hear back from them.
Having only owned a 300Tdi for a week, I'm only begining to learn.
