Thanks for the update! Interesting to see a B-17F (42-6011) with a chin turret.
The B-25B (40-2347) at Aero Trader still has a Mather Field code, "T-702", on the nose.
On your unknown codes page, the Yuma B-17 coded "U-48" (42-5741) is one of the YB-40s (named
Chicago). Here's another, "U-44", from
The Best Years of Our Lives: