I think they were all dealer installed. Not sure if they offered a receiver type or not, but I’m pretty sure they never offered a 2 inch full-size receiver style.
These were utility vehicles, but they were never meant to be very heavy duty in the Towing department.
And in 66, who knows? But that doesn’t look like an original by age either, unless somebody recently powder coated it.
Just doesn’t smack of 66 to me, but that’s just a guess.