I tried fitting a Mondeo fan (the slim design one) and there was no way it was going to fit.
I spoke with Kenlowe and their 17" fan will fit. They have upgraded their controller to a new automatic, two stage, electronic thermostat from the older in water sensor type automatic temperature controller. The new thermostat has a fast acting contact probe that can be simply inserted against a tube in the radiator. It's expensive, £150+VAT for the entire fan kit direct from Kenlowe. Paddock sell it for £110+VAT but make sure which kit it is, old or new.
Like me, other TD5 owners I've spoken to aren't using any fan at all, which is fine during the present weather but I would'nt be so confident in the summer...