It would probably need a substantial rework, as tricycle L/G and taildraggers have pretty different requirements in terms of the geometric location of the cg and the point of contact of the wheels. It has been done on a few planes, notably light general aviation, but those were probably fixed installations. In the case of the P-51, you'd have to find suitable structure for the nose gear to attach to - that's usually the firewall, plus you have to have room to stow it when retracted.
Then you need to get the mains behind the cg. if you take a bottom planform view of a P-51, you will see it's kinda hard to do without reworking it a whole lot. What you need is something more like a T-28. Same manufacturer, but you will see that the arrangement of elements is very different.