EZ outs are brittle so if you can use a punch to shatter what is left in the hole. The guts of an old injector are great for this sort of thing.
Then you need a guide to keep the drill bit straight. A bolt the same diameter as the stud with a hole drilled down the centre with the drill bit your going to use. Trim the length of the bolt so about 10mm of the drill sticks out. Wind a nut down the bolt to the thickness of the manifold flange.
Put the manifold back on, put the guide into the hole in the manifold and drill.

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