can you offer a tip how to get rid of a mustang on my six when im below 13,000 ft? should i start praying to jesus that he overshoot?
You don't need to pray to Jesus. You can deal with a P-51D on your 6 with mere tactics and throttle work.
If you have a little separation, say around 600-1000 yards, decrease throttle, dump flaps and execute a nose-low turn with full rudder. As soon as you see him losing angles bring the flaps up, engage WEP, and roll your lift vector in the bandit's direction.
If he's right on your butt, at <600 yards, use the 47N's superior roll rate and turn radius to out-scissor the 51D. Don't make your defensive scissors completely flat; use 3 dimensions. This takes timing and practice, but once you get the hang of it, it won't seem like a big deal.
P.S. If you don't already have them, rudder pedals will improve your defensive BFM dramatically.