Option 1) A regular scope will in most cases throw off regulation, but you might find a 'scope load' if you're a reloader - I did find one after some experimenting. If you consider a scope at all, especially with a fixed mount that eliminates the iron sight option, then I would strongly recommend you install an Aimpoint red-dot scope with x1 magnification. Those are so light that regulation should not be affected, and they will work for fast target acquisition as well as up to 100 yards with no problem. They are parallax-free also (unlike some other red-dot systems).

Option 2) At take-off option exists: Look at the HeymUSA website to see it on their doubles - it is a German claw-type mount that lets you put your scope on and off and does not interfere with the iron sights. However, this is very expensive and should only be done by gunsmiths that know how to do it properly.

Option 3) A .470 is basically a 50 yard gun: I have a detachable scope on it, but I don't even use it anymore even though my eye sight does not allow me to see the rear notch properly anymore. I still am able to hit the '10' at 50 yards - you just develop a proper mount that always stays the same, and then you don't need to see the rear notch anymore, you shoot the gun like a shotgun.

I suggest you shoot your 470 plenty before even considering a scope, it is not needed unless you have really bad eyesight - and then I would go for option 1 ... custom claw mounts or a H&H quick detachable mount will cost almost as much as your gun.