Hello Brian
I have a Dufour 44p from 2006 which is currently out of the water in Plymouth. You are welcome to come down/send someone to come and take measurements off the blade. I suspect Jeffa will know what size shaft they originally supplied and definitely worth a try. I had a new rudder made for a Classic 35 and they knew which shaft. Also look at the owners manual as it shows how many tangs it had as well as other info. Message me directly if you want to organise a meet up or discuss more.
Chris
The membership association for owners of Dufour Yachts