I talked to the crew of 76 which is the train that picked up 74.
When 73 was on its way to Charlotte, one engine died and they continued with the other one still running. After they got to Charlotte and were preparing to turn for 74, the other engine died.
As for 77, there were three engines available in the yard which could be used to make up a train. One was sidelined because of a vehicle strike from a couple of days ago. Another was sidelined because it was involved with a trespasser fatality the day before. We don't know about the third engine, but these trains all run with one on each end so they don't have to be turned at either end, so that was pretty much the ballgame.
jb