I haven't found any first hand source from before or during the March on Rome, but in the iconografic after, it looks like the source of inspiration was Caesar's March on Rome.
In the "mutilated by war house" built during fascit period (1938-1942) there where some mosaic representing Caesar passing the Rubicon and Mussolini's March on Rome (the latter is now lost, first damagedby partisan then demolished to open a door).
As you can see, the representation is really similar in iconografic.
To strenghten the link between Caesar and Mussolini there are a couple more of facts:
- first, is the interview made by Emil Ludwig to Mussolini, in which Mussolini said that for him Caesar was the greatest main in humanity after Crist.
- second, in a message to a "podestà" (pubblic official) in Rimini in 1933 he wrote:
“La statua di Giulio Cesare che ho deciso di offrire alla vostra città sarà
eguale a quella in bronzo che sorge in Via dell’Impero. Se possibile, la innalzerete sulla colonna
dalla quale Giulio Cesare parlò ai militi della XIII legione dopo che, tratto il dado e varcato il
Rubicone, ebbe deciso la marcia su Roma. Ogni anno agli Idi di marzo voi avrete cura di adornare
con fiori la statua del fondatore dell’Impero Romano”
The statue of Julius Caesar that I have decided to offer to your city will be equal to the one in bronze that is in Via dell'Impero. If possibile, you will rise [the statue] on the column from which Julius Caesar talked to the XIII legio's soldiers after that, cast the dice and crossed the Rubicon, he decided the march on Rome. Each year at the Idi of March you will have care to adorn with flower the statue of the founder of the Roman Empire
(note: all the link are in Italian, I've not found any english source)