I purchased a rifled slug barrel for my 11-87 years ago, but opted for the rifled sites. It was only good out to maybe 60 yards without a scope on there. I've since purchased a good scope. I haven't practiced beyond 100 yards, but I was hitting within 3 inches at 100 yards with the scope. With the rifled barrel and rifled sites, the rifled site would take up the whole deer ad then some at 100 yards. So forget about shooting much farther than 50-60 yards unless you mount a good scope on that rifled barrel.
Definitely, don't use an un-sited in gun for any hunting. You'd be better off with your existing barrel and pheasant bead if you can't site the new set-up in...