Adding an O2 Sensor question

[conoco]

Could anyone tell me when adding an O2 sensor if I need one on each header or just below. I was looking at ordering the edelbrock kit. But if I only have 1 sensor i didn't think I would get a true reading. Any help or explanation on how to make this work would be greatly appreciated.

My current set up is long tube headers and supper 44 series mufflers on each side. There is plenty of room if I do need to add 2 but didn't know if they should be wired together . It would kind of defeat the purpose of making sure each side was good ( I thought)