I think there are only a couple of officially supported locations for Ultramatic cars but any number of other solutions by owners or mechanics have been devised. Here are springs at the two locations the parts books mention --details vary on later cars but same location.
While it would appear Packard only had one spring on the firewall for 51-4s, I have seen springs at both places on the same car -- as well as several other solutions. Will be interesting to see if any other factory looking places turn up.