Not mine, just a lead:
https://www.ebay.com/itm/1963-Cadillac-Model-62-Rare-Dealer-Installed-Fiberglass-Hardtop/192613081825?hash=item2cd8a262e1:g:EiQAAOSwE0JbX1mj (https://www.ebay.com/itm/1963-Cadillac-Model-62-Rare-Dealer-Installed-Fiberglass-Hardtop/192613081825?hash=item2cd8a262e1:g:EiQAAOSwE0JbX1mj)
It sure doesn't look like a normal "GM" fit to me. Even on a "dealer installed" item. Gaps everywhere, even if it's "just sitting" on the car. (Before I deleted my comment on "a two door hardtop" I had gotten hung up on the "Riviera" nameplate.) I still think it ought to fit better even not snugged down. Is the sail panel sitting on the wrong side of the top bottom?
I guess it was marketed towards convertible owners up north who wanted a warmer, quieter ride in those cold winter months.