Just me being dumb, but to be clear we are talking about 2 different P-51s here?
Ser no unknown, code GO-Z, or GQ-Z. 355th FS, 9th Air Force. Modified in the field by removing a fuel tank, fitting a second seat and apparently reusing the cockpit aft-side transparency panels; note that a mechanic has to climb onto the wing to let the General out. Well worn drab paint finish, invasion stripes. Flew Ike as a passenger in France in July 1944.
43-6593, code S-WZ (or probably more correctly WZ-S). 84th FS, 8th Air Force. Modified to 2-seat configuration at a main MRO facility with a bubble type 2nd canopy. Unpainted metal finish before and after repair and retained the same squadron code, presumably not operated across the Channel after its repair as no invasion stripes apparent. Used as a squadron hack.
2 supplementary musings on 43-6593;
Dual control? I'm guessing not, due to the complexity.
Origin of the second canopy? Doesn't look home-made.