The artists impression seems to have a fuselage gun, plus one in each wing plus provision for rockets.
The 2 seater TP-51D 44-84610/84611 and 45-11443/11450, 6 accepted in July and 4 in August 1945. According to the USAAF delivery logs while only P-51M 45-11743 was accepted, 45-11744 to 794 and 45-11838 to 50 and 45-11893 were completed, the stage before acceptance, the interest is 45-11893 is marked as TP-51M. As the T says the two seaters would be trainers, it would seem there was at least a plan to have some for trials.
Why the 4th Fighter Group needed a night fighter is unclear.