OK Tac. I dug a little deeper and found this paragraph regarding droopsnoot operations that sheds some light on the 6 bomb loadout. It's from WarbirdTech Series Volume 2 Lockheed P-38 Lightning by Frederick A. Johnsen ISBN 0-933424-65-5:
Droopsnoot missions frequently were conducted at altitudes between 10,000 and 20,000 feet, at indicated airspeeds between 210 and 270 miles an hour. As reported by the AAF:"Loads have varied with the distance to the target. On missions of 200 to 250 miles, two 500-pound or two 1,000-pound general purpose bombs have been loaded, and some missions carried two 2,000-pound bombs without difficulty. A combination of external tanks and bombs is used when the range of the mission makes it necessary. Additional shackles may be installed to increase the number of bombs that can be carried. It was concluded by the Eighth Air Force that a P-38J, with leading edge tanks, carrying one 1,000-pound bomb and a 300-gallon belly tank, would have a range between 700 and 800 miles, at 20,000 feet and indicating 220 MPH (miles per hour)."
Whew! A lot of typing (for me anyway) for one relevant sentence, but I wanted to put it in context. The source given for the section in quotes is: "Droopsnoot", Evaluation of Air Tactics, Vol.1, No.1, The Army Air Forces Board, 17 Oct 44. So...what I get from this is that yes, adding more bomb shackles was a field mod but not an isolated incident of wild experimentation by a kooky mechanic/ground crew. It's amazing what you can find in a book when you do more than just look at the pictures.
