Hi James,
I am a pretty good shot with a smoothbore. When I shoot a fowler (without a rear sight and not a smooth rifle), I look over the plane of the barrel, not along it. If you do the latter, the heat waves will ruin your sight picture very quickly. I look over the plane of the barrel and use the front sight much the same way that I use the tip of an arrow when shooting instinctively. My rear sight is the comb of the stock just like the position of my fingers on my face is essentially the rear sight for shooting instinctively. On a fowler, I want that comb to be just right so it guides the natural position of my face to the correct and consistent position, which is my rear sight. I apologize for this long digression but the point I want to make is that a good fowler needs to be fitted to you with more care than a rifle. Your stock blank is a little thin but it should work if you consider angling the bore of the barrel so you can achieve sufficient cast-off, if you need it, to fit the stock correctly to your build. Like a dueling pistol, a fowler should be the natural extension of your physique whether you shoot shot at birds or patched ball at deer.
dave