Forgive my ignorance of inboard engines (hence the need for a mechanic), but to answer your question... I don't know.
I crawled under my sink to check it out and it appears to be one of the lower, aft bolts that holds the manifold to the engine block. What I couldn’t tell was where it actually broke. Since part of the bolt came out, I am assume the piece that needs to be removed is in the engine and not the manifold. If that’s the case, then it couldn’t be drilled out on a work bench.