There’s also a small display of how mainline steam trains of yore used to deal with loading and unloading mail while travelling at full speed, courtesy of an alarming-looking system of nets and spikes.
Indeed, and a visual overview (and demonstration) of that (among the other things, including sorting in the train) is available on youtube, movie is called "night mail", original from 1936, and available here: https://www.youtube.com/watch?v=S7SD6qt0EFI
The whole post office inner workings are an impressive and elegant system, I have to say. Very well organised.
I for one will be paying the museum a visit, although if 5'11 is hard to fit into the mail rail carriage, I suspect squeezing my 6+ ft frame will not really be possible :-S