I think that if you can find an original E-2 or E-3, that would be nice. It's definitely the direction I'd go for a complete restoration. But you can use another speaker while you're searching for an Atwater Kent. You'll need one with a built-on plate matching transformer or add your own. All the old tube radios were built that way.

As for the voltages, according to the schematic, the Model 49 used 67 volts supplied by an external power unit. It provides power for the tube filaments as well. If you don't have a power unit, you might look for one while searching for an Atwater Kent loudspeaker. In the meantime, you could possibly build one to get you going.

Wayne