I wonder if, assuming the OD of the barrel and bore relationship is thick enough at the breech, you could not drawfile the top flat and tang down a little bit at the breech end, blending in the height reduction a ways down the barrel toward the sight.
if done carefully I think that the only thing that would show would be a very slight taper to the top two quarter flats, and it might not really be noticeable. Even if it was a little, with the lock in place it would hardly show on the lock side. On the off side an engraved name or something on the quarter flat would create enough visual distraction to hide it.