I have thought of doing that.
It would be great if you would try it and report back.
The old guys were not fools. There may be a reason they kept the oversized Routledge bore not constricted.
I think the idea of being able to use the rifled barrel, and have good patterns with 12 inches of smoothbore later, is a great idea.
My thinking on it is that the rifling isn’t all that deep and wouldn’t be that hard to ream out, except the first 12” or so with the chamber.
The jug choke in the bore end would be easy, and if someone shot a solid bullet through it wouldn’t hurt anything because there wouldn’t be room to tumble or do damage to it.
You could polish the inside of the barrel and try it before you put the jug choke in it. Then machine the jug choke a little at a time until you get the pattern to want.