Steve,
You are right about the L&Ns use of the Monon RS-2s. They supposedly renumbered them #260 - #268, but I have only seen photos of #260 (#51) in use on the L&N. It was retired in 1972, so it worked on the Monon less than two years. Three of the RS-2s (#52, #54 and #59) were converted to L&N slugs #2063, #2064, and #2065 in 1972 as your book indicates. I have photos of all three slugs as numbered.
The others (#53, #55, #56, #57 and #58) were probably never used on the L&N and were traded to GE in 1972. The mystery still is which one became Altos Hornos #143.
George L.