So I just flew a simple test to look at the numbers. I took off and did an AH full power climb to 20,000 feet with 100% internal + DT's and the heavy gun package.
With the fuel burn set to 2.0 I climbed to 20,000 feet and leveled. Once I got to 340 TAS I set for maximum cruise according to my P-51D-5 Manual.
It stated 2,400rpm and 36" MAP for Maximum Cruise, the ingame E6B gave me the following data;
TAS- 330 mph
Time- 150 minutes
Range- 831 miles
Do you really need to loiter for longer than that in the MA?