A detail I just noticed —

One of the design principles that seemed to first appear in the mid-60s modernizing of locomotives involved preventing engine crew from passing between units while the train was in motion, by taking out the folding walkways on the ends of hood units, and replacing the chains at the handrail with a solid bar to eliminate the walkway path. This seemed to have been the case on all hood units and switchers by 1970, and probably earlier.

The chain was supposed to be connected across the walkway space normally, to prevent falls, but I believe it was possible to connect the chains from two adjacent units together to prevent falls off the side of the walkway while a crew member was transiting between units. (Like anything else, who knows whether this was ever actually done in practice.) At the same time, the diaphragms were mostly removed from the ends of F units, but that was much more haphazard and I have photos in 1970-74 with an occasional diaphragm still in place.

By contrast, any MP switcher, both existing EMD and new, got full handrails during this time instead of the little hood-mounted handrail that most switchers on any other railroad had.

Here is an ex-RI unit, which like practically all other American railroads had the chains as-delivered, and the chain was not only left in place but painted white. One wonders if those chains were replaced once the units got a formal shopping.

RG7