There are many reasons to rotate the engine mounting. One is to get the carb and fuel tank in alignment. The needle valve spray bar should be at the same level as the center of the tank, from the side. As for surgery. It's surgery. Long tweezers, screws threaded in from the back of the t nut just enough to lower it until it can be threaded from the front side. A corsair fuselage is pretty big around. You have got to have pretty big hands not to get down inside even a little bit. If that is true, you will just have to engineer tools to get inside. Patience and a little inventiveness will get it. It's not instant gratification.