Hmmmm......   The Voyager kit is not a sidecar, so that clause is not applicable.  Looks like a Savage-Voyager would no longer be a motorcycle.  The Savage part is registered as a motorcycle, but the combo is not a motorcycle.   Would that make the vehicle registration invalid?  It wouldn't be an unregistered vehicle, just a mis-registered one.  Talk about a can of worms.

The Voyager site says that any State motorcycle helmet laws still apply.  But the actual wording of the Cal.Veh.Code seem to indicate otherwise.  Pity I don't have the $4K+ for the kit and a lawyer on retention.