Ok, so I got it broken down and cleaned, ready for paint stripping, repaint and reassembly. The tilting of the head has been restored, as it was stuck solid. I tapped the head from the upright casting with a copper faced mallet and once out you could see why it wasn’t moving.
The bore that held the head in the upright was marred. It looked as if a previous owner had used a dremel or a file to take some burrs or dings out and had just made it worse. I used a cylinder hone to take them out and get an even surface. Now it‘s fine, rotates up and down and locks with the three nuts on the locking plate. There appears to be no slop / rocking in the bore, so I don’t think I’ve over cut it.
I believe that I’m missing two caps for the oiling points on the head casting - I have two that’s on the cover for the worm gear so hopefully I can copy them. And the lever for the direct indexing pin isn’t original. I think this should be of a similar size and shape as the main rotation locking lever (tapered with a large and small ball on it). Oh, and a ball detent that should make the pin click in place. I should be able to source an appropriate ball bearing and spring, but I will need to work out what thread size and type the grub screw is that holds that in place. That’s been butchered to put a new screwdriver slot in it. I guess it was stuck at some point as when they did that, they managed to catch the casting as well. (See the second picture)