Hola The first FM's for the Imperial line showed up in 1964. And yes the radio is built by Delco. Even tho it looks as the Caddy/Buick built unit from Delco the face plate has differant sizing. If your '64 to '66 AM/FM has a operating problem you can use the GM model as a spare parts supply. I did this so that I could get my '66 radio in proper operating manner. The the other differance is the GM version does not use 8 ohms as the MoPar family of audio speakers and the antenna up/down switching is built into the radio. Rodger & Gabby cruzin the rows @ the salvage yd '47 De Soto Custom (AM w/single spkr) '63 Le Baron (AM w/dual spkr's) '66 Le Baron (AM/FM w/dual spkr's & reverb)