Actually the Far East Air Force was the pre-war designation for the US Army Air Corps organization in the Phillipines - which was disbanded in Feb-March 1942. Although the pilots and crews were absorbed into the 5th AF it was not FEAF, or 14th, etc, etc. Why was FEAF even a reference for you when it was disbanded just as the RAF Mustangs flew their first combat missions in ETO. So, yes as FEAF was disbanded in April 1942, I interpreted your connection of P-51s to USAAF units in the Far East (PTO/CBI/SWP, etc) versus Aleutians, ETO, MTO, etc.
I guess i should ask you to clearly define what you mean before entering into a discussion