The first English translation of Facundo was made in 1868 by the widow of Horace Mann; it was reviewed in The Nation.
I never read Diana Sorensen Goodrich’s book on Facundo but I should. She had a very good article in American Literary History, “From Barbarism to Civilization: Travels of a Latin American Text,” on the reception of Facundo elsewhere; I kept a copy of it for a long time (having made this copy before JSTOR existed) but it is one of the files I am recycling because I do not look at it.
It seems that Americans saw the federalistas in the Confederates. The original article is from 1992; it is in ALH 4:3:443-463 but is apparently also chapter 4 of the book. (I would adore to give a seminar on Facundo and Facundo scholarship.)