Sounds like this loco has been bouncing around without a box for a long time.
Good eye on the poor repairs.
My favorite pilot truck spring is the conical spring that Mantua used on their General and other heavy steam of during the 50's and 60's . I keep a bunch of them.... I can send you one if you want to try it.
Regarding Diesels......... We have a local modeler that describes them well....... dismals.
It came in the original box and foam but it sure bounced around somewhere. I have a few of the conical springs and they are very good for stuff like this but thanks for the offer. I also have the old Mantua General with three cars, still in the see through boxes!
I had a friend who referred to diesels as "Diseasels".