you can change the rear speakers to 6x9s by using 90-91 parts.as ds says the radio module is seperate from the climate controls.try googling.some caddys used modules with seperate amps.
i have a new icm,new wires,new oxygen sensor,new fuel pump relay,cleaned the plugs,and checked the coils according to the repair manual.i had several bad coils but kept the ones that owmed out right.