Hi Zak, yes i think you are probably correct,.
Here is the scoop, the lady that owned my 65, fitted a cd player and Rockford Fosgate amp in 1998
Stevens Creek CA at a cost of $1050,
When i got it ,i fitted a Becker into the dash , and moved the CD player to un der dash,left amp where it is,
hooked up both antennas to both Becker and cd player,,yes just spliced into the one antenna.
love the Becker because it is user friendly,so easy to use with out taking your eyes off the road.
But i can also listen to fabulous 4 specker sound from the SD player.That small piece of carpet to hide
cd player,came with Kinder seat that this car also has ,but not fitted.