The Marines flew B-25s in the Pacific (PBJs) and the Navy operated B-24s (PBY-4) so I think Marshall would see 8th Air Force Corsairs as a trade. The Army can always give their Corsairs a different name like they did with the Dauntless dive bomber (A-24 Banshee).The good news regarding training is that the aircraft was very similar to the Thunderbolt (same engine, similar performance) so getting AAF pursuit pilots up to speed would be fairly simple. Most important thing is to leave them unpainted, and make damned sure no one says "Marine Corps" anywhere near Marshall.
How does P-48 Comanche sound?
Another good thing is that the Royal Navy was buying Corsairs for the FAA. The RAF might show an interest as well?