I have a photo of a 64 Belvedere.Might help.Spare was never out of the trunk.Car had 12,000 miles on it.The jack mounts to the right,should have brackets welded in from the factory to mount.
How was the jack post held in place? (Wingnut)?Yeah, if you look real close you can see the jack post to the right in the same place as Sixpacksteve's photo