I was going back over the chords for this song in light of the chord substitution chart from week 9.
That does help. It shows the song to be a heavy mix of chords from the key of A and the parallel minor key Am, together with exotic (to me anyway) chord progressions. I guess if it sounds okay anything is allowed.
After doing this I discovered that I do have the sheet music to this song so I don't have to rely on some guy on the internet getting it right (the chords above are right). It is written in the key of A (before the capo) with accidentals on C and G, which means it could have been written in the key of G. Which means it could be A Dorian ?????