Firstly, the synopsis given here is, as is so often the case, gibberish. Based very loosely indeed on the historical facts concerning the disastrous final robbery by the James-Younger Gang, this very odd western opens with a horribly clumsy bit of voice-over plot exposition, cuts to an unnecessarily prolonged scene of Robert Duvall on the toilet, and then spends its entire running-time lurching all over the place as it tries unsuccessfully to figure out whether or not it's supposed to be a comedy.
Cliff Robertson as Cole Younger, the nearest thing the movie has to a hero, is a huge, bearded lump of wood (offhand, I can't think of anything else Cliff Robertson was in), whose character development consists of being obsessively interested in state-of-the-art technology, mainly so that his technical expertise can get him into trouble in ironic, heavily signposted ways, and saying "Ain't that a wonderment!" far too often. Robert Duvall is an absolute swine as Jesse James, to the point where he's basically a cartoon bad guy who actually gets to kill people, and he gives his default over-the-top performance. Every other character is literally one-dimensional. Frank James is a nonentity who reads or quotes the Bible incessantly. Another gang-member is obsessively superstitious. And so on.
Much worse is the peculiar plot, which, after one reasonably well-staged gunfight near the start, ambles along setting up an over-elaborate series of absurdly contrived plot-points, while stopping for strange comedy interludes, such as a way-too-long slapstick baseball game that has nothing to do with anything. Even what ought to be the climactic shootout is badly mishandled, pausing repeatedly to remind us that almost everybody in the film who isn't an outlaw is a totally unsympathetic hypocrite, and give us a bit more of that "humor" which keeps popping up in the wrong places and isn't the slightest bit funny. And a lot of the overacting that occurs throughout is downright painful.
B-movie fans may enjoy spotting plenty of familiar faces (near the beginning, watch out for Valda Hansen, who was in Ed Wood's "Night of the Ghouls", in the very small rôle of "nude girl"), but this is a muddled misfire of a movie that never figures out which genre it's supposed to be in, and has no genuinely interesting characters. Also, it's a bit short on action. Walter Hill's "The Long Riders" (1980) shows us exactly the same events from exactly the same perspective, but it's so different that you couldn't possibly call it a remake. Which is probably why it's a much better film.