Thanks Michael,
Newbie error! 'Thought they were JPEGs – they were GIFs … Let's try again;



(my thanks to lathes.co.uk).
To reiterate, my problem is a missing support strap (not sure what it's called but I've marked it in photo 2 with a red blob).
What I could do with is a scale drawing (or tracing from the part) to get the dimensions, so that I could make up a new one from a bit of scrap plate.
Thanks again, Zeek.