I remember that in their catalog from the 80's. I thought it was targted at 77-78 Trans Ams. Unless you increase the handling of a First Generation Firebird, you may not need it.

I have only seen this in the catalog, but Craig Hendrickson (the H in H-O) in on PY's Board along with Ken Crocie who purchased H-O Racing Specialities. I belive Craig goes by "Original H-O" if I remember correctly. You might could pm him there.