A2A's P-47 and P-51 models are based on military (ie, combat) configurations instead of modern civilian configurations. Generally speaking, from about mid-war until the end of production the underwing pylons were installed at the factory.
Here is a photo of a factory-fresh Mustang about to be ferried within the United States by a WASP during the war:
I think that in the case of modern day Mustangs that many of the flying examples have had the pylons permanently removed, possibly because surplus military aircraft were sold to civilians after the war and used for racing.
Here is what appears to be a wartime photo of P-47s outside the Republic Aviation factory:
It is important to note, however, that the very early production Thunderbolts -- the P-47B and P-47C series, and early P-47Ds up to the D-15RE block -- did not have underwing pylons and so could not carry bombs or drop tanks under the wing. Later P-47Ds had strengthened wings and underwing pylons as standard from the factory. An exception to this rule is the P-47M series, a limited production of exceptionally fast Thunderbolts introduced at the end of the war; these were not fitted with pylons at first.
