Very cool to share this. Often there is no good reason the manufacturer changes small things except so it won't fit between models. Thanks for sharing.Registered just to post this, as I've been struggling with finding any info on it myself... I just replaced the rear upper balljoint on my UCF10 1991 with a replacement part meant for UCF20 (1994-2000).
It fits, apart from one detail, the snap ring groove ends about 1mm higher. I ended up grinding some metal off the control arm from underside of the seat.