You stated it looks like there was a tag on the door frame that had been removed. Were on the door frame was it located?
As Vaughn said a 64 will be on the side about halfway between the latch & top (this would be the drivers side.) The 66 would have been located on the top dead center.
If you can see were it used to be, this alone should tell you which year it is.
You would have to wonder why anyone would remove the VIN tag.
