Hi Stef,
Thank you so much for the link, I do appreciate it. It gives the details of the engine but no reference to ages. SO using the email link I have sent them an email in hope they can help.
I had a similar problem dating a David Brown tractor. It offered a total number built during each year and since I knew the year of manufacturer I could estimate how many were made per month and that gave me a rough date it came off the production line.
So hopefully the reply will be favourable and again I thank you for the link. It has been saved on my list.
Cheers John