1940 Seeburg Commander

Hi, im hoping someone can help please? i have a 1940 seeburg commander which i am restoring. it is 115v and the amplifier should be 830-3. the box doesn't work and the amp that came with the box is a 720a but was bought separately by the previous owner? before i spend money on having the amp repaired will this amp work on the commander?? another problem i have is there is no speaker and im thinking about buying a new speaker to fit but all i know is it should be 15", does anyone know how many watts and ohms the speaker should be? Many Thanks to anyone who might be able to help? Colin