Hi Norman.
Read this: http://www.bmw4life.com/suspensionLowellFA.htm. Page 3 should help out a lot.
The shock and spring need to be removed from the car and a spring compressor needs to be installed prior to removing the top nut. I'm not sure how it was possible to lift the parcel shelf without pulling the rear seatback cushion. Four or five black plastic push pins hold in place. If the car is newer (~ > 94 or so), the rear parcel shelf is backed with a fiber/cardboard type material that bends and cracks. Older cars have a plastic fiber material that would shatter before it became otherwise compromised. This is important to investigate because a bent fiber/cardboard type rear parcel shelf will *rattle* over bumps.
And believe me, it's annoying.
The center belt recepticle is held in place with an integrated (into the seat) retaining clip. Remove the four plastic nuts and lift the bottom part of the seatback cushion towards you, then reach behind the receptical and manipulate catch to get it out of the holder.
best, whit