The British only took delivery of three P-38's. After testing they realised what a dog it was and cancelled the rest which mostly went to US training units in a variety of mod states. Depending on who you believe the lack of turbos is given as due to the shortage of supply, or at that stage of the war the US ban on the export of turbochargers. The Brits wanted the engines to be interchangeable with those of the Curtiss H.81A Tomahawk, which had been ordered in great numbers, hence the engines being same handed.
The prototype had outward rotating props. Have seen no authorative account of why the change in rotation to inward. The engines of the prototype were fitted with failure prone epicyclic reduction gearboxes and subsequent engines had spur reduction, difficult to see that that may have had an influence.