I'm pretty sure Noveske's 6.8 barrels have a gas block seat that is just long enough for the gas block, then the barrel steps down to a slightly smaller diameter after the gas block face.

What I'm trying to say is, I don't think you can put an FSB on one of his stainless 6.8 barrels because an FSB is around 2" long - the front "ring" of your sight base will be a loose fit since this portion of the barrel is smaller.

Might wanna call and verify that.