not sure why you are doing any internal work to achieve 250-260rwkw. Standard engine will achieve over 300kw with standard internals, anyone telling you that you require internal work is kidding themselves. Standard Genuine Nissan head gasket is all you need, but if you decied to pull the head off anyway make sure you upgrade your valve springs as these are the first mechanical component to max out. You can then upgrade cams, run a kimetic gasket if you decide to change it. run thinner as to lift comp, which will help with mid range torque.