[billjam]

Keith,
From your explanation, I can't visualise how your belts are being affected by the cabrio roof, but I would assume that the top belt mount is on the parcel shelf the same as a coupe.
First pic shows the coupe rear parcel shelf mounted belts and the one below shows the retractable lap belts that you would have to use if you have to change to this type.
I have changed several cars from the lap type to later lap-sash type specifically to pass inspection, so if you want to see what the lap belts look like, drop me a message, I have a couple of sets (v cheap).