Nothing I've read indicates that the fuselage tank installed in the B/C models was smaller or different in any practical way from the one placed in the D/K models. The problem starts and ends with the assumption that the fuselage tank should always be filled, when it was intended to be an
overload tank used only when filling the wing tanks and carrying drop tanks would not provide the range needed for the planned mission.
All Mustangs provided with the overload tanks were marked with a white (or black, in the natural metal aircraft) cross above the data stencil on the left side of the fuselage, just ahead & below the cockpit sill as a reminder. Of course, that information didn't always get to the units (or sometimes individual ground crewmen) in the field and they had to figure it out for themselves, but that is a natural fallout when your shortest supply lines are over 4,000 miles (Dallas to Liverpool) and your quickest means of duplicating documents is the mimeograph machine (
http://en.wikipedia.org/wiki/Mimeograph). It was definitely well known and understood by the time veteran units started converting to the P-51 while still in combat operations, and issues or problems due to it being full in combat were most often due to individual error, not common practice.
In any case,
when filled, the fuel in the overload tank was
supposed to be used over friendly/neutral territory on the way to disputed air space and be more than half empty by the time contact with the enemy was probable. Since
Il-2 Sturmovik's game engine does not allow for a CG shifting due to fuel or ammo consumption, the CG should be shifted to one consistent with a nearly-empty overload tank, and 100% fuel should mean that the overload tank will not be filled (and who needs it on any maps in this game anyway?). Overload fuel should be an option for the Mustang, just like 'extra ammo' is an option for the P-47.
No doubt there will be some further issues with handling (there always is), but the Mustang used to have a pretty good reputation for good handling and responsiveness before the
Il-2 Sturmovik sim series trashed it.
cheers
horseback