The shutter size is fine, they just need to block the view under, over and to the side of the shutters, and block off reflections onto the viewed side of the shutterglasses from the back and the sides. Classic torchwelding style glasses would work, I guess. Hey if you need to wear silly glasses, anyway...
Very classic looking but not the cast aluminium of yesteryear:
I am sure these could also be made in shocking pink;-)
Or do something like the manufacturer did on the side of these, all around the smaller shutterglasses, to keep them less expensive but close them off in a somewhat more stylish fashion.