Just to thank folks for their help - this could have carried on for months with me ordering the wrong bits, but armed with the facts (rather than my deductions) I found out that the part is not available through Ducati as it is no longer in their supply chain. My thanks to Cornerspeed here in the UK for the trouble they went to, checking with Ducati UK etc. So I got on to Baines Racing (them of 'Imola' fame) and they managed to source a second hand one through phoning around people they now. Most impressive, and pleasing.
Anyway, thanks to all - hopefully we can now get my mate's bike back on the road, and out of my garage! Assuming that one day, it ever does see tarmac again, I be sure to post pictures - it's going to look great, even if a little offensive to purists....
Doug