You don't hear about O-ringing so much these days on Jap engines. But in th 80s it was always advised for turbo conversions. But in the 80s people used to weld wastegates shut and stupid stuff like that.
A standard head and block of most Japanese twincams, with a good stainless or copper head gasket, can take very high boost.
Also these days, with better boost control and ECU's, you may not have to drop the compression.