I'm working with John Voss on his Fuselage Codes site, and he sent me two shots of AT-23 converted Martin B-26Bs. Both are coded Z:

42-43338

Maybe 42-43376?
The Z field code is usually associated with Las Vegas AAF, but all Vegas planes we've found have all been coded "Z-###", sometimes without the hyphen. This style seems to correspond to the style used on Eastern training commands (first letter=field; second=squadron; third=plane number), but none seem to use Z as a field code that we've found.
Does anyone here have a record card handy for either of these planes? That would help answer the question. (For what it's worth, the background doesn't look like Las Vegas to me.)
Over to the experts - thanks!
_________________

All right, Mister Dorfmann, start pullin'!
Pilot: "Flap switch works hard in down position."
Mechanic: "Flap switch checked OK. Pilot needs more P.T." - Flight report, TB-17G 42-102875 (Hobbs AAF)