This is a study of the Cajun approach to playing the harmonica which seems to have first been recorded by Arteleus Mistric on November 7, 1929 and later by players like Isom Fontenot and my dear brother Mr. Jerry Devillier, for whom this song is named. Key to the Cajun approach is playing lots of splits that outline the chord changes and keep the rhythm pumping accurately with the breath pulse. This is exactly what the single row Cajun accordion is doing. It is basically tuned just like the harmonica. Check out the Filisko Tongue Block Trainer if you need help developing accuracy with your splits.
What you don't need is bending for the Cajun part of the song. Another adjustment needed is now thinking of cross harp (2nd position) being played from holes #4-8 instead of #1-6. You should re-familiarize yourself with the nose push (NP). You will need to develop the habit of dumping air out of your nose while playing notes out of your mouth all the time over the I chord. If you are struggling with the breathing and being too full of air, you may want to highlight all the 6 hole split-4 exhaling NP notes on your music. Your nose is the equivalent of the accordion air release valve.