Aye nev kev,
Not sure with the 1990 onto an older handlebar. But with the choke lever beneath the unit it doesn't have to rotate around the bar as it does on the older twin shock models. My hunch, and it is a hunch, is that if the handlebar diameter is the same on both models, this would be useable. But it isn't my dosh, so if you prefer to 'hang fire' for the proper unit, will keep the eyes peeled.
My regards, Bill.