Why? The P-51B can carry everything it did, is a lot faster, especially at altitude, and has a longer range.
Why do we need an underperforming P-51? They'd have to model an all new airframe (3-Bladed prop, scoop on top of the nose, nose guns, dive brakes) for a plane with no real use outside of scenarios.
Its only benefit would be as an earlier Pony in an RPS setup, but it would be used as a fighter 90% of the time, and not as the ground attacker its meant to be. Think the Il2 to the Nth degree.