If there are any casting numbers at all inside, let us know. If not, probably a Japanese knock off of a swept back antenna. Usually mounted on the trunk lid in the middle. Pairs would be mounted on either side of the trunk opening. I have deen this dealer option for Ford Galaxies(1963) and Edsels(1958). They look similar to the ones you see on 1958 Impalas. Sent from my LG-H830 using The H.A.M.B. mobile app
Ford accessory, 1955-56 They are now reproduced. They were very pricey a decade ago, now not so much https://www.ebay.com/itm/Rear-Deck-Radio-Antenna-1955-1956-Ford-Pass-Car/202179165691?fits=Year:1956|Make:Ford&hash=item2f12d13dfb:g:IW0AAOSwMQBaDIou&vxp=mtr
55-56 Ford rear mount as shown, is correct. I also saw one on a 54, mounted in center of the trunk lid, But I think it was not factory installed.