See if JHP has some 50mm headers kicking about or if you can get some cheapish if fleabay or something. A full 50mm system combined with the cams and PC will release a few horsies...
Combine that with a Brembo Radial Brake Master cylinder...
and finish off with getting your forks and shock revalved/serviced by either JHP or send it off to K-tec/maxton.
You should be able to do all that for £500...and pick up some rearsets or a new set of tyres with the dosh left over!