After much chin scratching and thinking, I came up with my solution to the seat belt issue.
I decided to raise the rear tub by 4" and create a new, much stronger 'B' post. The original 'B' post is basically a piece of flat steel 1.5mm sheet with a slender reinforcement brace behind it. I have effectively raised the top seat belt anchor 195mm, almost 8".
The top of the rear tub is now exactly level with the highest point of the scuttle, purely by accident. There are several side benefits of this approach. I have a much enhanced capacity in the boot, the rear passenger has a better seat with better back support with more enclosure, I also welcome the more 'upright' and higher profile which makes it more closely resemble the original 1930 Alfa Romeo lines which the Berlinetta is said to be modelled upon.
I have used 120mm X 80mm hollow section with 5mm wall thickness as the material for the 'B' post. While it may be a little over the top in some ways I know it will be man enough for the job and since this is safety critical I will accept the slight weight penalty. Given it's at the back, a little extra weight over the back axle is not a bad thing anyway, in moderation!
I have tapered the box section down to about 50mm X 70mm at the top and when it's finished I will cap the post and blend in the corners. If I do decide to use a hood I will have a perfect platform on which to mount the hood hoops.
The first stage welding in the new 'B' Post.
The weld at the base.
This is the 'Before' picture with the black kneeling pad standing in for my shoulder...
The effect on the angle of the seat belt over my shoulder is to make it almost horizontal, even after I raised my seat 45mm.
The robust nature of the new 'B' post can be seen here.
It only remains to do the same at the near side and I can tick another task off my list.
I will be ordering the gaskets for the engine and gearbox soon, so I can start re-assemby, the metal for the bonnet and bonnet sides will be in at my suppliers now, so I need to collect that. That will provide another challenge, forming the louvers in the bonnet side panels. I may need to make a press to do that, I haven't decided exactly how I am going to make them yet. I intend to have a play once the 'B' post task is completed.
In the mean time I am doing MOT remedial tasks on my ex wife's Vectra replacing the front-rear brake pipes with the car perched on ramps in her drive, at least it's not raining, although snow forecast tomorrow. Big incentive to get it finished today!