As far as I know, this is the largest battleship ever discussed for the Regia Marina. The original article is included in Rivista Marittima’s October, 1921 issue, titled “La fase attuale dell’evoluzione delle navi da battaglia (studio critico)” (The ships of the line current evolution status – a critical essay) by eng. Ferdinando Cassone.
This can be seen as “Build to the limit” study, discussing the optimal solution for a battleship design complying for a specific displacement.
This sketch comes under two versions, whose main difference is secondaries’ layout.
The first one calls for these specs:
8 456mm (4*2)
6 152mm (2*3) plus an undetermined number in casemates
216000 HP for a speed 35 to 40 k. (18 boilers, 12000 HP each, 4 turbines 50000 HP each (sic))
According to the Author, the superimposed layout of the engines, with the boilers above the turbines would claim for the ability to get these specs within the 45000 t. limit, a different layout claiming for 57000 t.
The second versions gives up the centerline secondaries in favor of a more compact protected area:
The protection was not to be sacrificed, as can be noted from the section below with a main tapered main belt, 456, 350 and 150 mm, and a horizontal protection of 120+50 mm.