Another wrinkle: What constitutes "condition"?

I contacted a local A&P to do the condition inspection on the Fisher 404 I recently purchased. He owns two homebuilts himself, but has little experience with wood structures. Along with some easily corrected minor issues, he found one significant structural issue that I think is actually a deficiency in the original design, reported by other owners and builders. I have a plan to repair it, making some changes to repair the damage and make it stronger than it was originally (I'm not an A&P but as an aeronautical engineer I do have the ability to evaluate the changes I'm making). The problem is that from his perspective, the repairs I'm proposing are not "by the book" (i.e. AC43-13). He said, in part, "Since it is a non-standard approach and a major repair, I need you to demonstrate how it effects a repair back to the original plane's specifications without change to the flight characteristics... Using non-standard repair techniques will make you a test pilot. If I agree to sign off, that also puts me in the position of an approving design authority for a test platform. I am uncomfortable with that arrangement."

The change I'm making is actually very similar to the modifications other builders have made during the original construction. In that case, presumably he would have no issue with it. If the repairs had been made before he had seen the plane in its original condition, also presumably it would not have been an issue. I can't see him as an "approving design authority"; even the DAR at the initial signoff doesn't evaluate the design, just the condition.