It was the P-51D that had the bubble canopy. The main differenc was the P-51A had a1200 hp Allison V12 and the P-51B had a 1400 hp Packard V12. and the front scoop. The belly scoop on the B protruded from the body

other differences:

.........................P-51A...........................P-51B
maximum speed .....390 mph............440mph
range......................750 miles...........810 miles
ceiling.....................31,350 ft............42000 ft.
bomb capacity........1000 lb...............2000 lb.

Other than that I don't know much about airplanes except for how much Hydraulic fluid you can drain out of em before they crash.