411 Backrest fixing
 

On the backrest two tongues are attached on the upper part that drop into slots in the steel bulkhead next to the fuel tank.
How is the backrest fixed at the bottom?

Rear seat back fixing
 

On my 407 the bottom is fixed by a screw into the transmission tunnel, yes just one small screw. The top is the same, two tags.

On the bottom of the seat backrest there should be two metal lugs either side of the armrest about mid way across that portion of the seat, they are angled to line up with the seat pan floor and screw into place, if they are not there don't worry too much as the seat base will hold the bottom of the seat base in place , just seal the holes in the floor.The important ones are the top ones that hold the backrest in place in the event of a crash , if the bottom ones came into play I suspect it would be a game over situation anyway. If they are missing on your seat back give Graeme at BCCPC a ring as he may well be able to help.

Thanks for enlightening me! Yes, the backrest is hold in place by the seat base, but in my car, with newly upholstered interior, the seat base pushes up the backrest a bit. That way I can see parts of the fuel filler tube when I look through the rear window forward.
So, to avoid this, I have to fix the backrest also.

The bottom brackets on the seat base will hold it firmly in place as it will stop the seat base lifting it and if missing on your seat back hopefully Graeme will be able to help with some replacements.