Next step, form the rear flange of the inner B pillar.

(Apologies, I can’t really see what that is!) It’s meant to be a photo of the new flange formed against the flange of the outer B pillar…
Then cut the side section of the B - half done here.


I’ll probably stitch these two pieces together while the flange is clamped to the outer B pillar, so it retains its shape, then add it to that back plate. This should ensure the two halves of the pillar match up in a half decent way.
Meanwhile, thought I would check the remains of the inner B is roughly the right shape, and no it isn’t.
This photo shows a straight edge up against it, showing that it has splayed open at the bottom. Cue some persuasion to get it lined up again. Measurements of inner and outer confirm success.