I am not sure that I can accurately answer any of youir questions as this is an area that I have not studied to any degree. My guess is that the total number RLL Spitfires can only be determined by a study of the RAF "Movement Cards" for the Sptifire type. I do know that there have been several excellent studies done my members of the Air Britain research group. Here is what I can add:
1)There were a total of 244 Spitifres that showed up on the "Combined Losses List in the ETO.
2)Sptifires were returned to the RAF, several were transferred to the USN, and 96 were sent from former USAAF deployments to the French French AF in May 1945.
3)USAAF Units that were known to have flown Spitifres, other that the 4th FG, are:
several Squadron of the 7th Photo Recon Group, the 107th and 109th TRS of the 67th TRG, the 12th Photo Recon Squadron, as well as training Squadrons of the 495th and 496th Fighter Training Groups.
Sadly, I am not able to anwer your questions in any greater detail or with further information. Ted51