A Skylark is singing again....

[Inigo]

the string guard isn't a mere tin plate, it can be seen that it carries a tensioner pooley, that seems to be adjustable, as it is mounted on an intermediate steel piece which is then screwed onto the guard plate by two screws or something.... Can't be clearly seen... The steel intermediate part carries the bearing for the pooley, and has also kind of a finger to separate the crossing cord, preventing it from dragging on the other cord. You'll need photos of that part too... How interesting, and what a nice phonograph!

[Gramtastic]

After a few hours bodging in the shed, I have made a string guard with a tension adjuster ! I found a scrap of aluminium which I could cut with tin snips. I then made the slot init by drilling a series of holes and filing. The adjuster pulley is from an old Meccano set as it seemed about the right size ! Put it all together and ..... it played for the first time in probably 60-70 years or more. Don't think the new piece looks too out of place as I found old bolts to attach it.
It feels good to hear a machine play for the first time in years !!

[Inigo]

It's a nice repair. If you want to preserve the originality, just paint the additional new parts in blue colour or something, just to show your work clearly distinct from the original parts. As you have made them, they could easily pass for true originals!