Don't know what films Pound may have seen back then, but you're right to point to Eisenstein/Chinese written character.
Just to be clear, though: Montage simply means, in film parlance, cutting/editing. Eisenstein's montage was very specific, and I think it should more properly be characterized as 'graphic montage', ie he collided images based on their graphic qualities. Any cutting is montage, and the Hollywood silent films (since you asked about the 20's) used a particularly bland montage based largely on proscenium shots, drawn from theatrical conventions. They were just assembled scenes. DW Griffith is a noted mutation, as he is known for his intercutting of action sequences. The famous climax of BIRTH OF A NATION is the foremost, and earliest, example of this. Come to think of it, this might be relevant for Pound's method, if he did, in fact, draw from film.
Eisenstein wrote eloquently about his montage in a series of books, but his films are the best way to understand what he was doing.
Early French episodic films (Feuillade) were pretty popular and were a big influence on Surrealists, in all media. Wouldn't be surprised if Pound knew some of this work.
One would want to look at when and where these films were released, and what, if any, subsequent changes could be seen in Pound's style.
We know he liked Disney films in his deep Mussolini days, for reasons I've never understood. Also, an earlier thread on this list discovered that he saw some Stan Brakhage film(s) much later.
best, Jay Anania