Bronto, Can I ask what are your sources? I am also building the Tamiya P-51D and the general consensus I found looking at various websites, discussions and pictures is that yellow ZC was applied at the factory, but was often over-sprayed in the field whenever any work was done with green ZC. I have not found any source that said planes left the factory bare metal.
I'm at the painting phase for the wheelwells so very interested in the topic. Thanks!