The roll bar mounting was way too tight what with corrosion and the spring in the tube. I had to split the sockets right down to get the remains out.
To improve matters for next time I turned a couple of sockets out of thick wall tubing
And welded to the original mountings
The fit is much looser and just uses a simple bolt to hold the roll-bar in place
Sorry about the mess, I've cleaned it up a bit since then.