Frames twisted/flexed with the roads of yesterday. Cabs had the front area with springs to allow for some durability in road surface and frame flex. Same with the radiator and bed. Various spots.
The bolts with the springs should not be loose, there are frame welping also. So not much squeak that I'm aware of.
You're probably just fine today in how roads are and how we use them. Don't think I'd worry much anyway since you boxed the frame. It's a better frame then a model a.
T's flexed even better...
https://www.youtube.com/watch?v=m1rlyl8VZFM