I've been away from this project for such a long time I forgot I'd bought a replacement part for the front seat support.
(I was about to jump for joy)
Unfortunately I haven't bought the correct part - well may be I was taking a gamble on a slightly cheaper bit?
As you can see in the picture I've got 123 610 04 20 instead of 123 610 01 20
The differences are quite large =>
1) Big curve for the outer part of the floor pan on both sides of the support
2) Seat bolts slightly more outboard than they should be for this car
Back to the drawing board eh? I thought I was about to save myself some time - it appears not