Smitty,
I hate to burst your bubble about having a gun with two barrel sets but the fact is that they really don't work out all that well, for several reasons. First of all there is the problem of having sighting planes that are at two different heights, the shotgun being somewhat lower than the rifle sights, even if you get them down as close as possible to the barrels, there is a difference. Rifle stocks also tend to be longer than most shotgun stocks. This is because they are fired by two different methods. Slug guns fall right into the rifle category if sights or a scope is used. Then there is the weight problem which I am not going to go into here.
In my opinion, the two barrel sets with one rifle barrel set and one smooth bored set, just don't work out that well. For one thing, if you are hunting when there are several seasons open, lets say Pheasant and Deer seasons, I can almost guarantee that no matter which barrel you have installed on the gun at the time, when game is encountered, you will have the wrong barrel on the gun. The only gun I have used that could have worked out well in cases like this, was a drilling that I used to own. Unfortunately, we are not allowed to shoot deer here in Iowa anymore with a rifle caliber, and even when we could, it was Does only! Bob