Thanks for the replies and the links. The research continues.
To clarify this will be done via the LAA. I don't think it will be allowed under the SSDR and I want it to be cleared for aerobatics.
I am interested in the 'external engineering' process really. I would like to know what level of expertise is required and how much could possible be done by myself providing calcs and using CAD and FEA tools rather than a sacrificial airframe etc.