Anyway it was straight forwards a free working out how far into the wishbones the ball joints need to go. I'm working on 50mm from the centre of the ball joint to the end of the wishbone.
This was my first attempt (on the left) but it doesn't fit very snugly so tried again using part of the tapered end of the cover. About 15mm is tapered and the rest isn't giving a total size of 50mm.
It sits nice and tight now. I put it together as above and then wound it into the wishbone using a bit of leverage when required.
And that's it. Repeat for the other side (minus the initial error) and I'll be happy in the knowledge that if I do run a child over the nuts and bolts won't graze it!