I did try a version of the Ger/CB/1915A (E1-1) with 40SHP/ton

With 40 SHP/ton machinery, the Ger/CB/1915A (E1-1) had machinery that would fit into available space. That produced a boiler room length of about 215ft and engine room length of about 150ft. The depth is actually greater than my drawing, so I could use higher boiler rooms and engine rooms. Those lengths would be divided into multiple engine rooms and boiler rooms.