Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Mustang shared appearance with most of inline-engined fighter; apart the engine, it shared next to nothing with P-40.
but the P-51 was drawn-up on behalf of the British by those familiar with actual Me-werk..
A laminar flow wing adopted for the Tempest series had a maximum thickness to chord ratio of 14.5% at the root, tapering to 10% at the tip.
True - that Laminar Flow is near impossible holy grail for WWII methods, but the Mustang fill and prime and sand undercoat was far superior to other metal fab techniques. The primary point to make however is that the profile drag in the wing tunnel was about 40% Less than the 23xxx - so not hard to extrapolate that even absent laminar flow that the 45-100 had accompanying superior boundary layer to turbulent flow transition which resulted in reduced profile drag.
Further the location of the max T/c provided for a more gradual velocity gradient from LE to max T/c which explains the delay from Drag Divergence to Critical Mach shockwave despite having a much fatter wing than the Spit. I don't offhand know what the Tempest wing T/c is - but that is the single most important factor - all else being equal - to Mcr point. The Mustang shock wave originates near the max T/c which is 25% Chord farther aft from conventional airfoils of the day.