Looking at the online photos, I would not be too concerned about serious damage to the Swanton Locos.
Until about 2000, the ASME Boiler Code required all welded boilers be baked at 1100F for about an hour to relieve welding stresses. Boiler steel, (think firebox) operates at continuous temps around 800F without metallurgical damage. I saw burned paint still on the tenders rather than discolored warped steel. Unless the journal boxes caught fire, it probably is just a nasty clean up job.