Thinking about Johnny Cash and hoping he's doing ok - IMHO, his best train song was on Marty Stuart's cd, he did "One Last Ride," and Doc and Marty did the breaks - I don't think it gets any better.
Also, I think the Carter family book says that AP was walking along and he heard Sara singing "Engine 143" - he followed the sound to her door - and the rest, as they say, is history. Shame they just were not more suited to each other in other ways.
Chris