Seat out, bottom mounting removed, 3" extension strap fitted, seat back in and perfection. I now have the buckle dead centre and about 1" adjustment either side.
Looks great, pity no-one will ever see.
I then strapped in the passenger seat, for the first time ever, and found it was exactly the same, it is impossible to get the buckle centrally positioned on the body. Obviously all my passengers have been too polite to point it out
So another extension piece on order so I can do that as well.
Later. Belt arrived, fitted, so now passenger has full adjustment available and can centralise the buckle.