Moved on to the downtube shifters, which are a bit of a mess. The clamp is Huret-Sachs, the shifters Shimano SY20, a very early index shifter that I dimly recall asking the bike shop to fit for me. YouTube told me that the clamp probably had to be re-tapped to accomodate the larger Shimano bolts. Anyway ...
The biggest problem was the index mechanism itself (circled). It is pretty rusty, and there was no easy way to remove the nut. I tried to force a bit of grease between the two plates, and maybe that helped a bit, but moving the lever is still quite gritty. Least satisfactory restoration to date.
I have asked for help on Reddit, and the answer may be a new set of shifters. I'm not too bothered about keeping everything original, as I know these shifters are not original, but the cost soon mounts up, so I would rather avoid that.
Not much more to do on components; the bottom bracket, clean the front fork, paint the frame, the wheels (not sure about the cassette; might get that and truing the wheels done by a professional), replacement bearings for sure.
Not much difference visually, and only a slight mechanical improvement.