It was actually planned but never developed:
P-51E: designation planned for Dallas P-51 But not used, aircraft completed as P-51 D-NT
XP-51F (NA-105): lightweight model (9,060 lbs)
Structure almost completely redesigned
V-1650-7 twelve-cylinder Vee liquid-cooled Merlin w/Simmons automatic boost control for constant manifold pressure
5635 lbs. empty, 7610 lbs. Normal, 9,060 lbs. max,
466 mph @ 29,000 ft, 4.9 minutes to 19, 500ft, service ceiling 42,500 ft
Four 0.5 wing mounted machine guns
Redesigned cooling & hydraulic systems
Low-drag wing w/straight leading edge
Three completed, one to RAF