I play this tune in -Eb-. On harmonica I am playing the 1st verse on an 1847 BOLD (LowBb) that is Country Tuned. This gives me the major 7th without an advanced technique. On the 2nd verse, I use a standard (Bb) and play the overblow on hole 5 to get the major7th.
It should be noted that the song uses both the major 7th and the dominant 7th.
You can purchase the 1847 BOLD (Low Tuned) harps here
Have questions about overblow or any other topic, email me here