If you really need the extreme accuracy of a rifled slug, you're better off using a rifle.
I'm by no means an expert, but it would be like building rifling into a muzzle brake and using a smooth bore rifle. It's the principle of having an entire bore rifled versus just the tip giving it a "spin" before it heads downrange.
I've never used a rifled choke, but I still get great accuracy using a cylinder bore choke and an EOTech and Federal slugs. But if you intend to dedicate this long gun to slugs, then it would be in your best interest to just buy a rifled barrel.