I used Brent's method this time and it worked well. Although with my tap combo I had to open up the access hole a bit. Worked great though
I do think you could go one size smaller NPT, but having one size for all passages is convenient too.
As far as the set screw, I think it would work great too. Drill only deep enough to leave a small step and then finish with a bottoming tap. It would tighten against the step and seal as well as NPT.
However, in the end, Brent's method was real easy and worked well.
As a side, prior to doing that one, I used to double freeze plugs there, not sure if it added insurance, but it made me feel better