Hey Ian,
Thank you. I appreciate your comments as I always find your thoughts useful. I hadn't thought about using a capella. I find that quite an interesting idea and I'll have a play around with it because I really enjoy a capella music. My all-time favorite group in this genre is Tonic Sol-Fa. Below is a link to one of their songs. It's a pity they don't have too many on YouTube.
Oklahoma Wind: Tonic Sol-Fa plus
here's the lyrics.
All the best with your songwriting

Noel