On the early cars like mine if the rear sprocket was simply spaced over a bit so that the centre lines of the two sprockets were aligned allowing an outer flange to be fitted, then I think it would foul on the swingarm but I haven't tried to find out. I do recall a post a while back where someone had got their one converted to the later spec, two flange rear sprocket at some considerable expense. Sounded like a lot of parts had to be changed.
I'm pretty sure there is no cush drive at the back - presumably the belt is supposed to have a bit more give in it than a chain (though I have my doubts) and the compensator should play it's part as well in damping out shock loadings. Use to wrap the rubber blocks in bits cut out of inner tubes to get the slop out of the cush drive on my race CBR600 - worked beautifully.
