Blue V......Looney Toon's advice is worth noting. If you want more power, engine & transmission issues are vital. You will need to plan your project otherwise expect eventual breakages.
Eureka & myself are both modifying our cars to a high spec and it becomes a long term project.
Also consider a realistic budget for yourself. Big power = £'s....... lots of £'s.
Up to 380 - 400bhp isn't too bad. If you are aiming at 400 - 600+ it's big bucks mate.
My block & internals are virtually the same as the Gobstopper and I am still restricted to just over 400bhp until I replace the box / prop / diff /drive shafts / suspension / brakes etc.