Koni's and Ground Controls will work fine with your 5th gen.
4 Wheel Steering came on the SI from 88-91
And as a special order on the SI's from 92-94.
I had a 91 with 4WS and it was just as everyone else says AWESOME.
After buying the 95 that I have now it took me about 2 months to be able to park straight. I was used to being sideways halfway into a space then cutting it all the way and getting it lined up. I tried to find a 4th gen with it when I bought a new car but was unable to. The reason they quit is because not enough people were special ordering it and it cost a lot for them to make. If more people knew how good it is I bet more people would have gotten it though. Hope this helps.