I cannot imagine how you could re-tap a hole with the same thread size at a new angle and not make a mess out of it.
If it were me I would drill the manifold a tiny bit vs. making a mess out of the block. The *correct* repair is drilling a bigger hole and using a repair stud that has threads one size bigger.
So if you think you can drill and tap for this repair stud with the engine in place, that would be the best way to do this.
https://moyermarine.com/product/dril...s-oblk_06_446/
