Never on a street car, but i have used them on dedicated track cars. There are two types, ones with nylon blocks and ones with bearings. I used the bearings ones. They should be inspected regularly, so I don't know how well they hold up to a street car that may see inclement weather.
Alignment during install is critical to prevent binding, so on an E body that would mean making sure they line up with the spring and not the frame. E body springs are not parallel to the frame. You also want them in a plane from spring eye to spring eye, and not necessarily flat on the frame rail either.
When I used them it was on a chevy. After taking all teh measurements, checking alignment and making some templates, we made a mounting plate that was welded to the frame, then the slider was bolted to the plate. Sorry, not many pictures from that era in my album.
