Randy you don't need to have something in writing to know something is amiss. Common sense says the dive flap would produce some drag, that drag is going to slow the airplane…really no ifs, ands or buts about that. The big unknown is "how much".
This is what I have found particularly exasperating about this thread. We can infer how much. Anyone with an intuitive understanding of aerodynamics (including you colmbo, apparently) would reasonably agree that a 45 degree deflection of airflow followed by another 90 degree change in close proximity at the apex over such an extensive span is going to produce an awful lot more separated turbulent air than the streamlined bomb / drop tank pylons of the Mosquito, for example (other less significant causes of drag notwithstanding).
The drag might indeed be mitigated in the presence of localized supersonic flow or a pitch change of the wing in a very steep high speed dive (I can imagine very strange things happening there) but even if that was the case the drag would still anounce at lower and indeed cruise speeds where the flow is completely subsonic.
Since the Mosquito's extra drag is observable, the absence of any extra drag with the P-38L dive flaps deployed is
clearly an omission, most likely by oversight (although there are at least two other possibilities).
Campaigning that the drag is negligible (with no evidence) or that no change should be made without exact data (also therefore no evidence) surely results in less realism by having absolutely no drag at all?
Or is my logic terribly flawed? Obviously I have to ask because I have a complex now about being wrong
all of the time