Well, Q, I've looked at that version lots of times, but there's something there I've overlooked until you posted it. I was probably misled by the lack of capitalization of "cap'n" in the original. You supplied it, and then I saw it.
"John Henry went to Cap'n Monday"
Without the capitalization, this says that on Monday John Henry went to his captain. With the capitalization, "Cap'n Monday" becomes, possibly, the man's name. The historical man was Captain Dabney. "Monday" is one of a couple of plausible mutations of "Dabney in the record, the other being "Tommy."
Thanks. That is part of what made my day.
The other part is finding death records for Cornelius Stratton "Neil" (or "Neal") Miller. His Certificate of Death indicates that he died on March 16, 1930, in Hinton, WV (probably hospitalized there, I think), of "bronchopneumonia" and "influenza," at age 68 yr, 9 mo, 13 days. Birth date: June 3, 1861.
In the spring of 1869, when he said he went to work at Big Bend Tunnel, he was about 7 yr 9-10 mo old.
Unless he was working at a tender age indeed, he did not work at the tunnel while it was being bored.
He said that he started work there at age 17. That would have been ca 1879, well after the completion of the tunnel in 1872.
I won't claim that his testimonies for Chappell and Johnson were fraudulent, though they could have been (perhaps he was pulling the legs of these professor types - he was an old farmer himself). More likely, I suppose, is that he conflated various memories.