Not to be argumentative, but I don't see that style of barrel as being a hinderance to good wing shooting. The fit of the stock is far more important than having a tapered barrel. If one shoots with both eyes opened one will see the barrel easy enough, not only the top of the barrel, but the barrel as a whole in relation to the bird as it flies.
Proper wing shooting consist of putting the primary focus on the target, and secondary focus on the barrel. One should not attempt to sight down the barrel, but merely point it. If the stock fits well, and you are consistent with the mounting of the gun, focus on the target, shoot with both eyes opened while tracking with the barrel, you should not have a great deal of problems.
I am no expert, but I have shot skeet competitively while in the Navy and am familiar with wing shooting basics. I admit I have not fired a shot at a flying object with black powder, but I have a similar barrel on my fusil and I have practice mounting the gun and following birds with it in flight. I do not anticipate I will have issues with how the barrel is set up as I have no difficulty keeping the barrel in its proper perspective in relation to the target.
Again I mean no offense, just my 2 cents.