Mel,
Interesting question. The power plant, from what I read, should have been an Isotta Fraschini Zeta, with 24 cylinders, indeed, in X configuration (IIRC). But I may be wrong.
In about two hours from now I will give the clue -- also because it was by far not a silhouette -- and will let you continue this marvelous thread (I am always open to - and thankful for - corrections, whenever it is needed)
All the best,
Paolo