When I ordered a new Chevy pick up in 1976, I already had a stereo radio to put in it. I ordered the truck with out a radio, but had to order a RPO package that included the windshield antenna, otherwise the truck would have come without the antenna in the windshield. Dont know if it was that way in 70, but that's how it was in 76.
By the way, windshield antennas SUCK
! At least on AM radio, and that was about all there was in this part of the country in 1970.