But I think both of those examples of 12ga. revolver are in a fairly important way "doing it wrong" when it comes to recoil handling - and general ergonomics, for that matter.
When firing a pistol, every millimeter that the line of fire misses the center of mass by is torque on the weapon, and every millimeter that the line of fire misses the line of your forearm and wrist by is torque on the wrist of your firing hand.
When you have the barrel elevated far above the handle as these examples show, I'd expect wrist-stressing torque to be generated, whereas a barrel with the least possible elevation above the handle would result in a simpler straight-backward kick that I'd expect to be easier to deal with.
So if I were to design an oversize revolver, I'd probably have the revolver cylinder rotating about an axis even with the bottom of the trigger guard, putting the barrel at about the same elevation as the barrel of a standard revolver and the cylinder forward of the user's grip. This also has the benefit of being - sleeker? I dunno. I think it would look better, more 'designed' than 'cobbled together'.
If you tell me you want it in a breakover style, then the support for that axis is going to be projected forward from the bottom of the grip and up in front of the trigger, with the pivot point at its forward end. That puts the hand inside a framed opening.
Of course, I'm given to excesses, and the other thing I'd immediately notice is that the size of the gaps between a circular array of six 12ga. shells allows you to drill additional chambers for .38 special cartridges or something similar (has to be straight brass and not too big) between their outer edges. Those could be fired from a secondary barrel on half-stops between 12ga. shells. So your character could switch from one to the other by rotating it a half-stop, but then firing and recocking normally would move it a full-stop so it would continue to fire whatever it was firing.