Well, I changed the radius arm bushes for some new poly things. One of the large bushes was sliding left to right along its metal inner. When I took it off the inner metal tube just fell out. The other one was still intact.
Anyway, after a long struggle getting the - what looked like original - metalastic large bushes out (with chisel, hammer, sockets etc), and just pushing the small bushes out with sockets in a vice, the new ones are in, the radius arms are painted, and all put back together.
A test run of about 5 miles tonight showed a distinct improvement. Of course now I can hear all sorts of other rattles and bangs. And the clutch needs changing. At least the radius bushes were correctly identified as one problem.
Thanks for everybody's suggestions. A job well done!
Cheers
Dave