I wouldn't think that the weight of the engine block, cylinders, pistons, heads, camshaft(s), valves, valve train, induction system, and fuel and oil systems would be more than the single crankshaft.
That's my point exactly.
Also, some of the propellers had a gun shooting through the hub, and having the engine in the inverted configuration would allow the gun to be more in line with the pilot's view
Take a look at a cutaway of the DB600 family. Sitting in the inverted vee, the gun would be somewhere down around the pilot's kneecaps...!
In this configuration, the propeller would need a gear drive of some sort, which would lower the center of gravity still more, since the motor would sit even lower in the fuselage.
It did have. But in the case of the Me109 - it brings the centre of the prop down in line with the cylinder gallery.
The only think I can think of off the top of my head is some role the inverted vee plays in centering the floating cylinder liners on assembly....?