The six speakers are located in four locations. There are two speakers in each of the front doors, and two speakers in the rear deck. I don't know what size they are. I'd like to know as well.
In a related question, are they 10-ohm speakers? I think traditionally, OEMs put 10-ohm speakers in the factory applications and sometimes, you can get really good sound from a vehicle when you simply install aftermarket speakers, which are usually 4-ohm. Less resistance equals more signal I guess. I know it worked on my old Cutlass -- maybe it'll work in the Cadillac too?