Since Williams doesn't offer command control (Legacy, in your case), you will find this combination will not work unless the "B" unit is an unpowered dummy. Command control requires a fixed voltage (15-18 volts) on the track, and a powered dummy would want to start running like a "bat out of ****" as soon as power was applied while your command engine would be sitting there, resisting that motion, waiting for a command signal.
Chuck