This one is designated a 'Tractor 11', Model No. 11 VE. These were made from the late 1970's to middish 80's as best we can work out. 1983 would be the original engine; as Bushy says, the machine was likely built in 1983 or 84.
There is an Illustrated Parts List download available in the
Greenfield Manuals area, which is a pay access section of ODK.
The second file down, described as 'Tractor 5 to 11 version', is the one you need.
New parts availability from Greenfield will be limited at best for this one, as it's now outside their 25 year spares supply window.
Parts common to later models, such as blades, will be no problem. Bearings and drive belts are standard industrial types, and easy to source once you have the type number from the old ones.
