Wow what a great response, thanks everybody. I was thinking about this problem at work today, trying to think of a cheat!
What I'm trying to achieve is to exploit my outboards turning capabilities by moving the linkage nut towards the pivot point, 50mm should do it. I am also looking on equalling the steering from left to right (turns harder to starboard at mo). I thought at the weekend that I'd like to remove the bracket complete and replace with something new, but I couldn't face the consequences if it all went wrong, so what I suggest is this:
I am going to manufacture a piece of stainless with a female profile cut out to fit exactly on the end of the steering arm (this will stop the arm moving sideways), I will bolt this in place. The linkage arm from the remotes will then bolt exactly where I want without resorting to a possible engine strip. I will then if I'm not completely satisfied with the installation attempt the bolt removal during the winter months.