From "Moto Guzzi Big Twins" by Greg Field:
Neither the Fiat 500 engine nor the Mule engine was used as the basis for the V700 engine, however, and it's somewhat puzzling how the whole misconception got started, given the fact that the Mule engine was designed by Micucci, rather than Carcano. The fact is, all the V700 engine and the other two share in common is a 90-degree V-angle. "Comparing the head design and structure, the distribution, the displacement, lube and fuel systems, and engine crankcases is enough to demonstrate that the engines are totally different and come from different ideas" asserted Todero. Said Carcano of the issue: "The [Mule] engine has nothing in common with the V7. It had forced cooling system and was a 90 degree V, but it's cylinders, heads, and engine casing, etc., differed completely."
