Hi Frank, it was MACR 10682 which I found by searching B-24 losses for 12/17/1944 at
http://www.armyairforces.com/Data/MACR.aspx which gives the Group as "481". I then looked it up on Fold3.com but looking again (and zooming in closer) I see it's on the actual MACR form as 451st BG/726th BS.