For that large of a hole it would be easier to lay-out the hole, then chain drill just inside the line using a #40 or #30 drill. Then finish to final dimension using a half round double cut or single cut file. When chain drilling a hole I like to use a scribe to do the lay-out instead of a sharpie since you cannot accidently wipe off the reference marks. If you are careful and take you're time with the file, the result can be as good as a hole saw or counterbore. I often use this method on instrument holes as well and if you are patient the result can be a custom zero gap fit that looks great.