From what i have seen, you may just need a custom collar that butts against the gas block (don't quote me, cause i'm not positive). At the most, the barrel would need to be contoured fwd of the gas block to accept a collar.
The 308 OPS with a brake mount would be the 12th Model. We have one in stock.
12th 30 cal runs $950, and comes with Brake/Collar. Contour fwd of gas block, if required, would be $65.