Did a little more digging through Bodie's book and I think the best bet still revolves around the P-38's that were intended for RAF trials. I haven't read the whole section yet but if I get the gist there were actually two different models that were originally meant to go to RAF service. There were not originally contracted through the lend-lease program and the RAF effectively cancelled the order apparently causing some bad blood between Lockheed and the British government (I believe Lockheed nearly sued them in court).
Apparently only part of the order were retained in the export version that we hear about, no counter rotating props, and no superchargers (used the V-171C engines).
It get's a little muddled in that it seems a lot of this was going on right around and after the attack on Pearl Harbor so everything was a bit of a mess but I found the following bit.
Concurrently, there were 121 Model 322-62-18 (P-322-II) trainers that had been reworked at Burbank as part and parcel of the AAF contract that covered conversion of Lightning IIs into regular service type P-38F's and P-38G's.
All P-322-II aircraft were provided with V-1710F-2 engines (unsupercharged). Most pilot and mechanics associated with the P-38F-15 ir O038G-15 airplanes probably never knew tha they had been laid out as British fighters, and it appears that most of them were ultimately sent to combat zones.
That in of itself raises yet more questions (mostly about the super charging), but I really wonder if that airframe didn't begin as part of the RAF order, was painted then finished life in the AAF.