Ghost rings won't work properly with the rear sight that far from the eye. That's why they're set up with the rear sight on the receiver. Shotguns with ghost ring sights are considered by most folks to be single purpose guns, or at best defensive and large game hunting shotguns.
For removable sights on the barrel, just pick a combo with a rifle sight short barrel, or build a DIY combo by getting whichever barrels you like that include an 18 - 20" rifle sight barrel. That's the way I prefer to set up a 'do it all' shotgun - a 26 - 28" VR barrel with RemChokes, and a rifle sight 18.5 - 20" smoothbore barrel.
Like this one -
18.5", fixed MOD choke, parkerized finish, tritium sights