You're welcome Ron, I can't remember how they were assembled back in 1991 but I think it's pretty much the same as we do it today. I'm almost sure that the front cover has to be removed, which means that the balancer will too.
We currently insert the magnet from the back of the cam sprocket so the "blunt" nose part of the magnet that passes under the sensor protrudes out from the sprocket, which means that the "flat" part is flush up with the back of the spocket giving it clearance to clear the case back there as it rotates.
Maybe Andy can shed a little more light on this for you.
Good Luck!!
Jack