P/O.Eugene Q.Tobin Spit Loss
 

Hello
I am trying to find out the complete letter markings for the Supermarine Spitfire MK.VB W3801, that was flown by the American P/O. Eugene Q.Tobin of No.71 Eagle Squadron, who was shot down and killed on September 7, 1941 near Boulogne, he was victim of a BF-109 from JG26.
His aircraft was Presentation Spitfire POPOCATAPETL I from Mexico, I need to complete XR-???

Any help would be most appreciated

v/r

Santiago A.Flores