If you have not already done so, I suggest that you contact Scott Nelson with your John Henry information. Scott is a history professor at the College of William and Mary. He has suggested that the "white house" of some versions of "John Henry" refers to a building at the Richmon Pen. He maintains a special interest in John Henry at Big Bend and continues to work on this subject. He might receive your information with more enthusiasm than me.
Contact information can be found at http://history.wm.edu/srnels.html
I find Scott's suggestion about the "white house" to be reasonable - I've seen such a reference in at least one other song text (not "John Henry") in which it is clear that a penitentiary is meant. However, I suspect that this is an intrusion into "John Henry" from that other song, or another one yet, and not something of historic significance in connection with John Henry.
As you can construe from my other posts here, I strongly suspect that the further pursuit of the legendary John Henry at Big Bend will not be fruitful. I believe that the data of Guy Johnson and Louis Chappell come close to ruling out the possibity that John Henry did his thing at Big Bend. This does not correspond, of course, to their conclusions, but my reading of the data in their books leads me to the position that their data do not support their conclusions, which represent wishful thinking.