The other MK3 coupe at Alistair's factory had the shallower seat wells the same as on mine and the register did show this and my MK3 being later built so we think the Corby factory may have made this modification on later coupes to aid the fitting of the handbrake cable.
I wonder if anyone else was aware of this modification.
I only wish I had took my camera with me. (shame on me).
The ones on my MK3
95 by Roy Forrester, on Flickr