To give all specs is nearly impossible now. ASC was the main GM convertible conversion people responsible for the convertible cars fit-out.
Under the front seat area is a strengthened support rail on each frame side, a bit like a subframe connector or cheaper to make when in full production, etc.
It is important to note that the tops were NOT all the same exact dimensions between 88 & 92, and things like spring tensions, not being a power top.. spring tensions changed in 1991 also. Most parts like cables and latches are available one way or another..and may change from year to year too.. so its not always free or easy to get but like in any older cars restoration etc.. patience is an asset.
If memory serves correctly, the conversions were done in Los Angles at a warehouse next to the then big GM plant in Van Nuys that built the 3rd gen cars. (Went though the plant in 1989 .. they were then building around 800 cars PER DAY .. all sold.. 2 shifts...treasured memory that rare tour that was organised for a bunch of about 14 Aussie's.)
Some of these images may help.
