Thanks for that,
Ed,
I was going down the same road, however it's going to be difficult to change the pulley ratios, It has a 2 belt system, one drives up to the water pump, reducing rpm, and the second drives the alternator. the water pump suction side sticks out in what would be the path of a 'normal' operation, it's probably the history of the engine, the injector pump prevents the alt. going on the left side of the engine, goes back to the petrol forerunner I'd guess.
It was a free alternator and the repair kit for the whole thing, including bearings was €25 so if it fries due to overheating I'll have to come up with a better plan!
Glort,
I take the point about the hot engine bay, maybe there's a bit more free air under the bonnet of the tractor!
Cheers Stef