Only the engine block is the same. The crankshaft, cranks, pistons, engine head, valves, cams are Ferraris. After saying that, the Maserati V8 was actually designed by Ferrari to replace the current V8 in the F355 and 360. That engine can't be bored to bigger capacity anymore so the engineers had designed a new engine to replace it.
However since Ferrari took over Maserati and when Luca decided to re-enter the US market, Maserati had to find a normally aspirated engine in place of the turbo of the Maserati GT, in order to meet the strict US engine emission rules. So he decreed that Ferrari hand over it's new V8 to be used by Maserati. But the engine top, the valve arrangements and the firing order were all changed to fit Maseratis engine characteristics. That's why the Maserati engine sounds like a typical American V8 because of the firing order whereas the new Ferrari engine maintain the "flat plane" firing sound of a typical Ferrari V8.