1991 Indy 500 classic rear suspention

Any chance you can post a picture or two?

There were some different suspensions used and they vary a little bit on how to adjust them. As for a '91, it may not have that much "lift" available without adding some drop brackets where the rear mounts bolt to the tunnel.

I'm not sure about the classic but I can't imagine that it is much different than any other 91 500 or any other indy around that year. If you look at the suspension mounts (front mounts and rear mounts of rear suspenssion)there should be two sets of holes, one set higher than the other. The bottom rear mount will most likely be a drop bracket that has the mounting hole below the running boards. The suspension will be installed in one set of them. If it is in the higher (top)set of holes drop it to the lower one. If this doesn't work I would suggest checking the shock and springs. The old indys never did sit that high but it should sit higher than you explained.