A Great Eastern-sized Devastation class

What could be added if the 1870s Devastation class had Great Eastern's displacement?

It could carry about eight 12-inch guns in four mountings and gain considerable range, creating something like a very early all-big-gun battleship.

Most of the extra displacement would go into four twin 12-inch mountings and greater endurance. Raised barbettes or a diamond arrangement could manage the firing arcs, although the latter would be awkward. The result would be colossal by 1870s standards. Its concentration on a uniform heavy battery points toward dreadnought logic even though contemporary mountings were not yet modern rotating gunhouses.