Looks like they finally got the receiver extension right, at 7 5/8" internal depth. Lose the H buffer and that spring, replace with AR15 Carbine H3 buffer and Armalite EA1095 spring. Replace the too-short gas tube with the Armalite AR-10 Carbine gas tube. Since he already has an adjustable gas block on the way, measure the gas port diameter when the original gas block is off - I'm betting its 0.070" gas port diameter, which is too small for an 18" midlength-gas .308AR barrel with a 0.750" gas block diameter. Drill it to 0.080~0.085", then install the new adjustable gas block (the adjustable gas block won't be necessary at this point, but it's on the way, so might as well use it). Always test an adjustable gas block wide-open. Open the gas flow as far as it will go, and run the gun until it's broken in. Once it's fully broken in, then you can start playing with gas flow.
My $0.02.