Wheel Well Reference
I’m gonna quote from Dana Bell:
Dana Bell
Mustang corrosion control...
Fri Oct 1, 2004 08:33
160.111.69.104
You've got several options here, but unpainted "natural" aluminum with a yellow zinc chromate main spar is the most common for P-51Bs and Cs.
The early Allison-engined Mustangs used the standard prewar corrosion control finishes for the wheel wells and struts: two coats of primer and one coat of aluminized lacquer.
In 1942, before the Merlin-engined Mustangs entered production, North American was granted permission to build Mustangs without interior primers as a means of speeding production. The main wing spars were generally primed with a single coat of yellow zinc chromate to protect the alloy spar itself, to avoid dissimilar metal corrosion in the areas where the spar contacted the inner faces of the aluminum skin, and to reduce static electricity buildup on the aft face of the spar (where the main tanks were located). There is a chance that some early Bs and Cs were delivered with unpainted spars, but I've never found more than a slight possibility of that having occurred.