I don't know how I never saw this before, but Yawara and her Grandpa make a cameo in Project A-KO #3: Cinderella Rhapsody (1988) [ID2875CT]. It happens at 14:14 in chapter 5. They are customers at the fast food restaurant where A-Ko is working.

In addition to the 100 other cameos in that series.

I've seen plenty of references (Girl Ranma's hairstyle as A-Ko tries different styles) and parodies, but I haven't caught any outright cameos. Of course, my knowledge of late 80's anime is not that good.