Hi - I feel as if I could write a book on this. Sandy has kindly helped me out with the loan of a replacement.
My Magneton is also cooked and has been with an auto electrician for weeks whilst he looks for replacement field coils. I've borrowed Sandy's Bosch starter which has been fine but needs the larger spacer (i've used washers with no probs for the last 3 weeks). According to the auto electrician he believes the Magneton with separate field coils is not the best application given the 7s vibration and heat issues. He rates the Bosch with fixed magnets as a more robust solution. The part number for the Bosch is 0986018240 (ex Scorpio and Sierra 2.0/2.9).
I've ordered a new replacement for £78 from a mate. Wood Autos in Huddersfield will have one at c.£78 + VAT plus £ 7 postage....or your local scrap yard may have dying Ford's you could get a couple from....don't forget the bigger spacer though (or washers)
Rog