[link to original on tumblr]
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I had all of this worked out last night, but I wanted to check it to-day before I posted it. Sometimes it helps to check the studio recordings against live versions, and there is a live version of "I Must Move" on Zombie Heaven. (I think it'll be easier to learn the guitar parts from that since Paul Atkinson uses an electric guitar there. On the studio recording, he uses an acoustic, and at times it's hard to hear distinctly.)
While I was practicing this, I realized that it's an-other instance where Chris White uses a variation of D F#(m) G A (see also "Don't Go Away," "I Don't Want to Know," "Don't Cry for Me," "Brief Candles," and "The Feeling's Inside"). This is closer to D F#m A G though, but I'm not sure of the chords yet (most of the guitar part isn't straight chords, which makes it a bit harder to figure out). In any case, the bass part includes that D F# A G variation.