Gadge, I think most of the rim will require to be removed with approx 50mm removed for the front 300mm, this is both inner and outer wings. The recess that runs along the length of the car looks to be out over the new wing, it might fit if this is removed from the original Insitu wing. I am at the start of building a garage, well can't find any local builders interested in taking on the job, so this mod is on hold for the time being. It looks as if the new wing is the same dimensions and shape as the existing, not a tad larger to fit over the insitu wing.
Ralph