Just am idea , but what about fitting a serria rear 3.62 LSD 7 INCH DIFF to a transit mk6 , will it fit? Only got my transit last week but just love getting the best out things.
The Sierra 4X4 has a viscous coupling L.S.D. but has independent suspension so you would have to use the rear beam, suspension arms, drive shafts and hubs (4 stud) etc. I don't think it would carry the weight of a van body. It would give you rear disc brakes. Not really a viable proposition.
Dream on but keep your Transit standard and see how you like it first.
as i said just a idea , a bit of out load thinking. but what about the crown wheel and pinion i wonder if they are compatable? its a nice van dont get me wrong but it has a 5.13 rear diff, could just do with the revs being a bit lower on the motorway, but just looking for a cheap alternative.