I’m clueless on this one. Are they cast or are they plates welded together? If a frame is bent, can it be repaired or the part of another one welded onto it?
Anything built in the past 60 years has a welded frame. They definitely can be repaired by welding. The limitation isn’t generally the technology, its the economics. If you’re just running the last bit of life from a 3rd hand GP9, it’s generally not worth fixing a bent frame.
A wreck damaged GEVO would probably be worth patching up.
This certainly fits in with the aforementioned 60-year timeframe: IIRC, when EMD came out with their first switcher units, they were offered in both cast and welded frames: the SC1 and the SW1, with “C” signifying cast and “W” signifying welded.