I would discuss your needs with Karl, because although porting the head will ultimately give more power, it will lose some midrange. So it might be an idea to just do three-angle valves / seats. Karl will best advise you though on the spec that will be most suited to your needs, but you do need to sit down and discuss how the car will be driven for Karl to give his best recommendations. Also, you will have to push even a 0.63 a/r T34 VERY hard to get 400bhp on today's fuel, let alone a 0.55 a/r one .