It's actually just the top-right panel that you need to swap over ie the surround round the lever. I just redyed them with my dye so it matches the seat base.
The seat bolsters were rubbed down with wet and dry along with a magic sponge with acetone to remove the worst of the cracks/creases
Then a few layers of dye to restore the surface.
Another curiosity/problem is that the later seats dont have a bolt hole to bolt on the shoulder seat belt guide - actually explains why I see so many later cars where the belt goes straight from the reel which I dont like TBH.
Need to find a solution as to what to do with the belt guide - do I just cut it off and will I have to cut other side to match????!!!
Here's a comparison of the old seat back with a bolt hole for the guide, the matching back with hole and the newer style back with no hole for guide.
In the end I drilled 2 holes in the back of teh new seat back and threaded a bolt and washer from the inside to the out so I can put the guide on and then put a nut on to secure it (epoxied in place as you won't be able to hold the bolt head once the back is screwed in place.
Mock up before I applied the epoxy
All the screws for the seat back ready for painting
Once the bolt was expoxied in place and the new back dyed it was screwed back on the seat. To make things easier I used toothpicks to locate the holes - very fiddley job.
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