A T3.48 will be ideal for 300bhp, CR needs keeping std, lowering will not be needed.
I can recommend Brian Randal, of Hepworth, near Diss/B.S.E. area 01359 251888, for all machining parts etc.
I have a T3 compressor housing machined out with a T34 inducer, and a .48 turbine housing, boost starts at 1400, and full boost by 2500, just to give you an idea.
Got the be one of the easiest engines in the world to rebuild, so might as well diy, got any piccies of the mk3 ?, I love the mk3 tina, esp 2.0 GXL in red with black vinyl roof, and cosmic alloys.
tabetha