Rory, I put my Auto Orchestra in my Equipment "graveyard" in the bowls of my warehouse 10 years ago. Late next week, I'll try to find it. If it still works, I'll ship it to you, so your dad can try it out. If he likes how it works, you could then call AJ at Ketron to choose the modern equivalent. Dad can listen to downloadable samples of modern Ketron arrangers to see what's possible.
I'm not trying to sell the old unit, but It would be a good way to get him to try pedals.
All it would cost is the freight back here. I'll cover the freight to you.
Hope the thing still works..!
Russ