This aircraft was an old B-25D model (the upper turret is aft of the wing - see second photo by barneybolac) so is, by that stage of the war, most likely to have been a BG/BS hack, with USAAF units having moved to the B-25J model. That was certainly done by 5th AF B-25 units which were also on Okinawa in the same timeframe.
While the 319th BG was on Okinawa from July - Dec 1945 it was equipped with the A-26 Invader, so a B-25 seems unlikely even as a hack.
A better candidate unit in 7th AF would be 41st BG. That unit took its B-25 to Okinawa in June 1945. It moved back to the Philippines in Dec 1945. But the Group CO was a Col. Bywater. Maybe another senior officer in the Group?
Or maybe someone at 7th AF HQ?