I will have to solve this challenge on my Royale Sabre build which also has an upper mounting point too low to meet the current regulations.
The ROC chairman suggested one option is to use Mk3 MX5 setas that have a seat belt upper mounting intergated into the seat back.
Example picture below.....(I don't own these seats)
Mazda MX5 Mk3 seats by
marlinpeter, on Flickr
Presumably these seats are reinforced to take the forces in a crash situation.
I have no idea if these seats would fit in Berlinetta but offer it as another idea to consider.
BTW I'm enjoying your updates so keep them comming....