There's a sledding hill near where I grew up, outside of DC a few miles. It's long and steep. One night when I was in my 20s I was there with a girlfriend and my sled, and a group of guys came flying down the hill on a car hood while I was walking up. I stayed far away from that hood, and kept my eyes on it the rest of the night. I could envision getting sheared off at the ankles if I got in the way of that thing.
My 2005 Ninja 250's caliper is one of the part numbers that works. I looked up the part number for an '89 and some Google images of that number look right and others look a little different, with a different mounting bracket. If you take a good look at yours and compare it to a known one that's OK, you should be able to tell if it's right. Here's one that is the type that can be adapted with the instructions on the resource site. It's made to me mounted behind (the engine side) the right fork slider, so a spot on the disk comes past the small piston first. The left side version looks very similar, but the small and big pistons are swapped.