Yeah I'd say that has probably been done. I do vinyl graphics on the side. I have made hundreds of badge overlays of different things. It depends on how many you want as to what a sign shop will charge you. They will just need to get the dimensions. Most sign shops will do it. Some will not because of copyright laws if they do not own licensing rights for that running horse logo.
I don't know why but it just does not look right to me. It has a very added on appearance. It may be just because of this one image. If we had some shots from a few different angles it might look different. Also I think if the the oval were the color of the car that might look cool too.
With the right coloring I think it would look decent. Subtle but different. I usually tend to agree that nothing but the Ford script really works inside that oval but I think if done right it could be one of those smaller subtle touches that makes a difference.
Stick with Orig Ford. Custom emblems look tacky. It bothers me more then decals do. The best is when they cover Ford Ovals with "FAST" or "STEEDA". Those look just amazing