well thats what i have asked on numerous occasions even to parts and dealer staff and no one seems to know!!!!
apart from a few mentions on here from a couple of owners that have the boxes rebuilt there is no "hard evidence" that the synchro are "different"...
i have a spare box but dont at the moment have the time to strip it to have a nosey (it is an early box) - i have had a look on the parts system for the synchro rings/baulk rings and theres 2 types in the box on the parts list i was sent...