Just be SURE to slather those Manifold bolts well with Anti-Seize, so you can tighten them again later..
I HOPE you took the time to MATCH the Intake Ports
to the Head and gasket.. They usually do not match-up very well and After-Market manifolds are far worse, too..
Clean up the Exhaust manifold, too..
A Premium, Performance Valve Job will improve breathing too..