Arne and David, thanks for the swift response!
Arne - I have just spent a pleasant half hour/hour watching the youtube clips you sent me, Arne. I found them most informative, especially the information on Allen Farrell. I don't intend keeping the existing rig, but rather want to change to junk completely. I have taken the liberty of downloading most of the information you have published here, and will use it to guide me through the design process. And you are quite correct, that rigging point is called the hounds.
David - I suspect that I am going to have to go with a single mast and sail, given what you have indicated. The more I see pictures of rigs, the more I realise that the boom essentially ends above the coachroof, allowing a long sheeting angle to the battens, and I think you are right when you say that at 9m it will be difficult to squeeze two masts into her length. My doubts about a single rig is that the sail might be huge and therefore difficult to manage; I don't yet know, I have not sailed with it yet, haha!
The length of mast I quoted is above deck; the mast is currently in a tabernacle. once it is stepped onto the keel it should be in the region of 30' (9m) above the deck, which I suspect might not be tall enough...
What I can see is that I am going to have to do a drawing! At the moment I am reading PJR again and trying to formulate possibilities. Already the fact of discussing this idea with ye is having a beneficial effect, allowing the outline of the project to coalesce into something like concrete reality.
I am now living on the boat in Liverpool during the week (I commute to work there during the week) and so will have the time to do drawings, and being on the spot, take measurements. As I reflect, I think that the mast is about 25cm at the base, which is close to the PJR recommendations, but I am not there to check right now.
Thank you both for your help.
Jonathan