Dimished chords and autoharp are a tricky thing. Sometimes the major or 7th will work. Also it looks to me like a way-cluttered arrangement, especially for that simplest of tunes, the spiritual. Plus an autoharp stroke is much longer than a guitar strum, in terms of actual time. So when a guitar might be changing, you might be in mid-strum. So I would simplify it to the chords that carry the accented beats.

The melodies of spirituals vary with the singer, so since I am not hearing the melody you are hearing, I can only work from what you gave us. But you will want to fool around with it some I suspect.

Dm, C7, F, Dm, A or A7, Gm, A7, Dm, Dm, F, G, D or D7, A or A7, A7, Dm, F.

Arranging on autoharp is not hard, and neither is transposing if the chord bars are set up with logical sequences-- you just move your fingers over one position one way or the other. The final judge of the arrangment is your ear, so play around with it till it runs off your fingers clean and easy.

~Susan