Just an update in case anyone else is doing this. I completed the mirror installation yesterday by drilling and taping the original standard stanchion. The drill chart that came with my chain store tap and die set, said to use a 3/8" drill for my 7/16"-20 mirror post. After doing that, I tried to tap the hole with no success. The tap just wouldn't start. I called a machinist friend of mine and he said I would probably need a better quality tap (which he has). I took the stanchion to him and he had difficulty starting his tap as well. He checked his drill chart and it called for a 25/64" drill for the 3/8"-20 tap. After using this drill, the tap started and the job was successful. Two lessons learned-use good quality tools and make sure you have the right info. The chain store tap and the drill reference may have worked on softer metal but not on the stainless used by Henry. Apparently there were many areas where he did not sacrifice quality.