Okay here's a follow up.
Got some safety wire but couldn't find the spinning wire tool anywhere so when I tried to install it I couldn't get it to tighten properly with the confined space. I also tried forming a replacement shape from the safety wire thinking that might be close enough to work, unfortunately it's not 'springy' enough.
Then I noticed a set of old hubcovers, with a spring wire 'lock' on the inside. Whipped one off, cut it up a bit and then had 20 mins of bending, shaping flattening etc. I now have a good 'Heath Robinson' facsimile that has some spring and looks good till I can get a replacement.
By the way it was a '98 Aurora hubcover.
Thanks for all the suggestions
Dave