Join Golden Oldies if you haven't already, this group based in France has the mssion purpose of saving historical multihull racers, very helpful and friendly.
Look up the Brit A.Y.R.S. web site and go through back issues of the journal from the day.
Also in the UK look up Scott Brown Multihulls and get onto the forum archives, I think it is called the multihull.com .There is a Kelsall section there.
Look up old race accounts from the day, they were well covered and should led you to more connections.
Have fun! I'm sure Derek would answer questions.