Hi there, do you have the rear seat back that folds down? If so you should find two screws in the back piece. This holds the back to the steel plate that spans the rear towers.
You will also need to unscrew the parcel shelf at the front as the back piece fits under the return lip of the shelf.
I pritty sure its just two screws - not put mine back in yet.
You don’t need to remove the back seat, just remove the parcel shelf. There are three types of rear seats.
Early up to 68 +2 rear seats comprising of squabs, and separate back rest hung from a thin angled strip screwed to the parcel shelf.
+2S type of hinged down variety. Undo stud fasterners and tilt down seat back. This should reveal fixing screws. The whole rear seat assembly is a one piece moulding which sits aside the body centre section.
Third type +2S later and +2S130 reverted back to separate squabs to save weight.
Hope this helps. My car has the tilt down seat version but the original +2 squabs and back rest are in the loft (not for sale)
Thanks for your advice, I have fixed seat and I finally found the screws so the back seat is now out of the car. Now I “only” have to release the nut holding the strut in place!
Hopefully you are aware that this nut also retains the upper spring perch and the preload on the spring. Don’t touch this nut until you have compressed the spring with a proper tool. Sorry if I am belaboring the obvious.