OKAY! I'd call Hydo E Lectric and ask if they know where the hold down cables mount. They are convertible top experts! On my Dad's Catalina, there was a two piece block of metal about the size of an ice cube in the trunk. It had a bolt running through the center and mounted near the package tray. A small "L" shape slot in the block adjusted the hold down cable tension. You've done the research, but I still think it is time to call the installer and discuss hold down cables.