I went through this about a year ago. I contacted a lot of Hide Sponsors like Short Action Customs, Long Rifles Inc and American Precision Arms.
Their short answer was that they did not want to drill the gas hole for the gas block. They suggested that I get a Krieger blank with gas hole and barrel extension to send them or... call GAP. I contacted GAP and they were too busy at the time to take on the work. A few months later I contacted GAP again and they told me to send the parts.
In general: Is 0.75-MOA "good" for you out of an AR?? Are you shooting hand-loads or top-tier match ammo?
If Yes, Get a Noveske and be done with it. Their stainless barrels do 0.75-MOA or better in my experience.
The Krieger and Bartlein come into play if you have the ability to drive a gas gun to 0.25-MOA. Most don't have that ability! I'm not sure if I can either but, I have a Krieger to try and a Bartlein on the way.
Krieger vs Bartlein is a coin-flip. Excellent vs Excellent.
Good Luck,
AnschutzNerd