I'll follow your progress with great interest, Ian. Looks a great project!
I have my grandfather's Thornton Pickard 'Special Ruby'. It's 3½" x 2½" (1/6 plate?), so possibly like the other Steve's model. It has a Ross Xpress 5½" f4.5.
It needs curtains and a CLA, which I really must get round to some time soon.