They were around in the sixties, but from pictures I've seen not widely used on hot rods. Plain ol' coil springs with a separate shock were very common on rods back then.
The general answer is: The technology of coil overs goes back to the 50s when they started using them on MCs and it wasn't long until road racers started to adapt them to their light weight formula cars. In 1961 A.J. Watson used full sized C/Os on his Champ cars.
Saw a pair of very early looking coil overs on a '60 Chevy Bel Air a few years ago.. Don't know if they were factory but they sure looked it.
My old 48 Austin that ran D/G in the sixties and early seventies had Koni coilover front and back.Also had a four link with axle on the front.