Any squealing on cold starts? As said above, it sounds like a belt issue. Cold fluid is harder to pump. Add to that you say the pump was replaced. Check the tension on the belt and see what the pump actually does when you start. You gotta rule that out no matter what.

It’s fifty years old. If you take shortcuts yer gonna have a bad time. Pull the plugs.

Anything can be fixed if you have enough money. In reality though, this is a symptom of widespread and imminent structural failure. I’d guess that the other side is fixing to go anyway. And if it’s this bad up top imagine how the bottom areas of the frame are. Time for the glue factory.