You need to think in three dimensions i.e. a trussed design Of course, why didn't I think of that? The trick is how to get those very substantial trusses in between the main bearing bulkheads, between the head bolts, between the cylinder sleeves, and inside the main caps.
An aluminum block as stiff as cast iron is impossible.
Theory is fine, but a real engine development program ON THAT PARTICULAR ENGINE trumps theory