There was no P51B with 20mm cannons.
British Mustang Mk1A about 200 had 4 20mm. Used in army cooperation work and for reconnaissance. Basicly P51A or A36 apache that the british replaced the MG's with 4 cannon. It was still allison powered but fast and potent below 15K.
How would you like to see the summer sqweekers roaring through furballs HOing everything with these......
