Folk Melody is marked con moto, so be careful not to let it drag (my version runs around 92 bpm). In measures 9-11 and 25-27 I found it much easier to play the dotted half notes with the left hand thumb.  I found that playing those notes with my right hand thumb tended to impede my ability to play the upper melody cleanly, and making the switch didn’t seem to make the playing of the left hand more difficult. I should point out that in the phrases that follow (measures 13-15 and 29-31) my Dover edition shows the dotted half notes of the same voice being taken with the left hand thumb.