you'll need a ported head with at least new exhaust valves (not a good idea to use old valves for big power,standard size valves are fine) then some suitable cams for the spec.....your looking at a fair amount of cash really.

NMS do their own heads and they are very good,MADevelopments will also be able to spec one for you too,in fact a few tuners should be able to supply what you need for 500bhp...but it's gonna cost