If Stan Jones was a working cowboy, I have trouble believing he knew all those obscure chords mentioned about 6 posts above (Gm....etc). I sure didn't. I'm no trained musician, but I put the capo up 2 and play in key of A form and it seems to work out pretty well.
I remember when this song was popular. I was 8 years old and it was the first song that my young ears really perked up to when it came on the radio, which it did often back then (1949 I think it was).
I suppose over the years I may have the tune mis-remembered but I don't think so.