I can't imagine how much work went into filing up the forend metal, fitting the wood, cutting the side supports, and then mounting it all onto the action & bbls (it snaps into place using a standard Deeley-style push button setup).
BTW: The pic doesn't capture it well, but those side supports are sort of V shaped and one side is beveled at a 45-degree angle. Just one more way Boss went out of their way to make everything fit just right (and drive their gunmakers crazy).
You know Mr. Sumner loved receiving an O/U commission. Think of all the additional engraving time spent embellishing that foreend. The foreend alone contains more engraving than an average Boxlock. I bet he charged Mr. Robertson double the sidelock engraving rate!
Cannot get any better! I was told ,fanciful though it sounds ,that the metal helped stop rain getting into the works. Have had the privilege in coaching owners to shoot a good many of these guns. Never shot one I did not like. Thanks for the picture.