Those barrels (and every regular run barrel) are just a little thicker at the muzzle than was common on trade guns, but will really shoot a round ball well.
A 20 ga, 46" barrel is also good for a New England fowler from 1775 on. Before that, the barrels were longer.
It would make a nice, plainer Bucks County gun, many of which were smoothbores.
If you have the Grinsdale fowler book, you'll find plenty of inspiration. Look at the Fainot guns- they are really high on my dream build list (I dream I'll have time to build guns, but it ain't happening lately).