Interesting. The RAF experimented with the the Rolls-Royce Vulture 24-cylinder X-block engine (two Rolls-Royce Peregrine V-12 cylinder blocks) on the Manchester early in the war, and gave up on it.
The LW tried a very similar thing with the the Daimler-Benz DB 606 "power system" (a pair of DB 601 inverted V-12 engines side by side) on the He-177 about mid-way through the war, ran into several big problems, but kept on trying. Probably for too long.
And then... turbines. So post-war, all the largest of the huge recip engines died off pretty quickly, replaced by turbojets and turboprops.