Steve, do you know when that FRA rule went into effect? I've long noticed that the MONON seems to have begun applying the extra handrails mainly on the cab "cheeks" and "eyebrows" of their F-units sometime after 1952. They were originally painted to match the carbody, but eventually were repainted yellow during the early 60's.
There's a photo on Page 101 of your book showing a special train in the rain at the 1953 grand opening of the joint Erie/MONON depot in Hammond, and with #81-B still without those extra grabs. By 1955, all the F's seem to have them applied though.