Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
The intake manifolds are not the same for each side. Since the cylinders are in different positions on the crankshaft, the intake manifolds are slightly different in order to partially compensate for this positioning difference (the rubber boot that connects the velocity stacks to the air box take up the remaining difference). These photos should make it pretty clear which side is which.
S markings mount on the left side of the motorcycle,
D markings mount on the right side of the motorcycle.