Wyn Fellowes, member 'eurorover' , says that a Ford Mondeo pump fits and works just fine, but the pulley will need changing over from your old unit. He has done several cars. He could not recall which Mondeo model, but taking the pump to a Ford dealer is a good idea, since he should be able to say which model and year.
I know from Wynn that the pulley will need to be swapped by a power-steering specialist but that will be a much cheaper route for you to follow, I would think.
As I think has been mentioned to on several occasions, it would be a good idea for you to become a full member now that you own a 260. There is lots more information available in Forum sections you cannot visit until you do. It is not expensive to join the MGOC, when you think of all the benefits including the club shops, MGOC and Two-Sixties.
David