Have a look here for Mustang info;
The P-51 Mustang Variants: P-51D -MustangsMustangs
There was quite a market for refurbished P-51's after the war, another notable player was Temco (later LTV) who invented the 'TF-51' (not an official designation) which involved putting a second seat into basically a stock airframe but with a canopy of larger profile to give more headroom for the second occupant. Our "Miss Velma" at Duxford is this variant.