Now before you get carried away

The radio antenna was for a certain type of radio that they didn't use in the ETO. Just to make sure, I went through all my 51 stuff and can't find any ETO birds with that antenna showing. There would be a tension spring showing behind the cockpit armor plate headrest too. No go.
Pacific Mustangs, such as the ones on Iwo used another type of radio as well with two post antenna on the rear of the fuselage and one below the engine about where the wing starts. Again, no antenna wire or tension spring showing in photos.
Regardless, there was that antenna wire on many a Mustang. Part of the problem is it's way too thick
To be honest, I'd never have even thought about it, but I got reamed by a Mustang fanatic when I did a profile of an Iwo based 51 for him. He made it very clear there was no wire as the radio set up was different.
I've seen reference in photos about 8th AF ETO based 51s without it as well.