That block should be perfect to high hp turbo, it has all that is needed; both strength and good cooling. You should not expect headgasket problems, keep the max cylinderpressure fair. If you need more with O-ring, then you must make your own coppergaskets. Should not be a big issue either.

I am not sure how the titanium exhaust valves take the heat, but these valves are small and could be substituted with stainless steel.

Sounds like a good idea, if you need the power !