Sei Jushi Bismarck (translated roughly as "Star Musketeer Bismarck," or so Wikipedia would have you believe) was a series that had a rather understated cowboy theme.
You might possibly recognize it as being Saber Rider and the Star Sheriffs...
...which took that cowboy theme (if you don't believe me about this theme, take a look at the toy) and hit you in the head with it. How much does it do so?
Peter Cullen dusts off his John Wayne impression to be the giant robot. The dub version of the giant robot, if you didn't notice, is named the Ramrod, which apparently was slang among cowboys for being the big guy/leader in a gang. (A ramrod is also the device used in an older gun, such as a cowboy-era revolver, to drive the gunpowder and bullet into the gun.)
Taking it even further was some coloring storybook I remember having as a kid, which featured a really Western-style story. All I really know about the series from that, however, is, well, nothing. (I would never have known from that book that there was a giant robot at all. In fact, it wasn't until I started looking for this kind of stuff on the Internet that I realized, hey, giant robot!)
Something I did learn, however, was that April/Marian totally looks better as a redhead. And that the armor these guys wore looked really good in all black. Ahh, childhood!