Army, Air Force and Navy (and Coast Guard, Police, a bunch of others) all work.
It doesn't surprise me at all that the "Mustang" didn't work, because the atc_model is normally the ICAO model number for the aircraft so normally, say, B377 for the Stratocruiser, P51 for the Mustang, EC35 for a Eurocopter EC135 helo (that last one is off the top of my head, I haven't checked it, so don't shoot me if it's wrong!
The way it works, if anyone doesn't know, is as follows:under aircraft.xx
atc_id= the registration number of your aircraft (N5432B, G-MSTG, 533456 or whatever)
atc_airline = airline callsign (e.g. Army, Air Force, Speedbird, Continental, etc.)
atc_flight_number = airline flight number (eg "1" with an airline of "Air Force" will call you "Air Force One").
atc_heavy = tells ATC whether to say "Heavy" after the flight number/registration or not. 1 = heavy, 0 = not.under general
atc_type = aircraft manufacturer (North American, Eurocopter, Boeing, etc.)
atc_model = aircraft model number (EC35, B763, P51, B52, whatever...)
In general, if no atc_flight_number is specified, then FS will refer to you by your atc_id ("N9725D"). If there is a flight number listed, but no callsign (or the callsign is unrecognised) then you will be referred to just by the flight number ("1054"). if a callsign and flight number are available, they will be used to refer to you ("Speedbird 1054", "Air Force One", etc.).