I have a Killer Innovations Orias chassis with a Luth AR modular buttstock. I had a Surgeon 591 mounted in this for a year or so but Ive switched to all Manners stocks. It also comes with the NV top rail mount like shown in the full Orias chassis photo. I did have to mill out the trigger well to fit the safety on the Calvin trigger. Don't have a photo of the milling but if you're interested I can get you one.
Looking for $700 shipped. They are normally $800 without the stock or NV rail.