nvshooter, I bought my Wilson barrel undrilled. Then I assembled it on the receiver with hand guards and gas block so I could mark the exact location. Perhaps you can discuss that option with your barrel maker.
By the way, it's not only the gas port, it's also the location of the step in barrel diameter that the gas block butts up against. There is more to it than just the hole. That's why it may be useful to offer the whole upper ass'y to the barrel maker to establish the exact location for turning the step and drilling the hole.
See? This is why it is valuable to ask questions. So you can learn something from a guy who BTDT.