Yeah there were not a whole lot of American actors in the UK at the time. if anything UK actors were going to Hollywood not the other way around. At any rate the whole story is so goofy I think the British actors pretending to be Americans fits right in and adds to the charm. It is one of my favorite stories for all the wrong reasons.
One things that I will say in favor of The Gunfighters is that the main cast seems to be having a good time making it and that gives the story a lighthearted feel that I enjoy.
Oh and by the way,is it fall yet? I want to see the 12th Doctor on screen for more then thirty seconds.