[Note 491.1] The song was printed as a broadside by Harkness of Preston [Bodleian Library collection of broadside ballads Harding B 11(3157)]

mustashers - [Note 491.2] Railway companies liked to recruit ex-army men who they regarded as reliable and amenable to discipline. In keeping with that, the uniforms of railway servants were influenced by the design of military uniforms. From 1860 to 1916 it laid down in regulations that every soldier should have a moustache.

[Note 491.3] a "semberly" could possibly be a temperance assembly.
Railway mission in London were a major venue for temperance meetings.

[Note 491.4] Judith Flanders tells us that "there was a recognised hierarchy of door knocks" in London and quotes the German journalist Max Schlesinger who wrote "The postman give two loud raps in quick succession; and for the visitor a gentle but peremptory tremeol is de rigueur. The master of the house gives a tremolo crescendo, and the servant announces his master, turns the knocker into a battering ram…Tradesmen on the othe hand…are not allowed to touch the knocker - they ring a bell"

Reference
Judith Flanders, The Victorian City: Everyday life in Dicken's London (New York, Thomas Dunn Books, 2014) p86