Presumably it is a petrol engine so registering it as an agricultural vehicle is moot since you can't run it on red diesel. Your road travel would also be restricted to within 1.2 km of your holding.I've taken the decision to have one built for me on a late Jimny by Shropshire Quads. It wont be cheap but it needs to last so I'll pay good money. The only question really id how to ensure this and does it register as an agricultural vehicle or as a road vehicle? It wont be doing mega on road mileage, 10 miles a day tops so limited mileage is a chance.
As I get the beasty built I'll update.