Tuning the 4.6 V8 as fitted to the MG 260 models

[Beemer-5]

What are the popular tuning options for this engine? It appears to be very similar to that used in the Ford mustang, but puts out less power i see.
I have been offered an immaculate 2005 SE model for silly money and am toying with the idea of creating a 'sleeper' in time for next spring?
Any information welcomed.
Also the names of any specialist tuners please.
Thank you.

[Beemer-5]

Nick, apparently the car was £33K new, fully loaded, but is now available for £15K, just run-in. 2,800 miles.
It seems too good to miss and i would quite like a 'sleeper' with 400+ bhp.

[Beemer-5]

He virtually never uses the car, it's one of 5 cars he has use of and the MG simply doesn't float his boat, hence the low mileage.