The event which pmm1 refers to is run by the Vintage Sports-Car Club. I was until recently a member, but when I discovered that they were running (other) events outside the law, and were not prepared to do anything about it, I left. So, they are unlikely to be helpful to anything I say.
But it was a helpful suggestion, and thanks to pmm1 for making it.
Tomorrow I am on the track of a replacement shaft with a full compliment of cams, and I am likely to balance the cost against four years membership of the VSCC I won't have paid.
Tim