You don't even need to tap them all the way into the ports. I just get some short set screws, tap the holes about half way through, and run the set screws in until they bottom out. That way the set screw can't possibly migrate into the port. I still use a little loctite to seal them in. Just make sure the set screws don't hang out and interfere with the manifold or gasket, some of them can hang up on the exhaust manifold flanges depending on what manifolds you're using.
Some of the ones I drilled and tapped were already plugged with carbon, which is what will happen to any space left between the set screw and port eventually.
