Which Large Frame Lower ? I case you don't know, there are no meaningful "Mil-Spec" guidelines for Large Frame AR's .. so not every part is as "plug and play" as AR15's.
And ( IMHO ) a 6.5CM will be easier to shoot at 1K, less recoil, less drop and wind deflection then most 308 rounds.
An Adj. GB is a very helpful add-on, Dependent on your gas port size and / or location. Easier on the brass, you , follow up shoots, parts.. etc.
And... gas guns require more "training curve" at the bench then bolt guns... so plan on a decent amount of practice.