Just as a suggestion.
It is best to unscrew the vertical rear panel so you can get a hand onto the reel from inside the car, this helps once the bolt is removed and you are maneuvering the reel out, and feeding the belt and fittings through the slot in the fixing bracket. Apart from the nails in the carpet, and self tappers in the metal panel, there is also a bolt through to the cyclops light to be removed. I didn't remove the whole of the panel, just wedged it open at the top so I could get my hand in.
Ah, I was rather hoping not to have to rip off the heavily glued carpet off of that if possible.