That is the problem with machine shops in Denver. Way too stupid busy and can't be bothered with a small job. My thoughts are to use the cutter to get close to the diameter I need then use grinding stone to finish it.
Don’t forget to measure and get the throat set right at around 90% of your valve size or what you are doing is worthless. You can YouTube this procedure online and use a set of snap
Gauges. If you have never done this it may pay to practice on a scrap head. Slow and easy.