Advice for drilling on my intake wanted.

Soooo, I think my replacement exhaust manifold is one where the factory started using a larger bolt to mate the intake and exhaust together. I was trying to check port alignments against the new gasket that came today and the intake would not slide down onto the bolt on the top of the exhaust. I guess I have to enlarge the bolt hole on the intake. Anyone done this and any bit recommendations for drilling that cast iron? Pics...