I work with radios for classic cars, and a customer wants new speakers for his 1959 Fleetwood sedan..

The front is easy -- 4x10, and plenty of aftermarket speakers are available that fit perfectly.

The back is not so easy. According to Custom Autosound's chart, it says "1959-66 Convertible use a DVC-3015" meaning a 5x7. Original rear speakers for many vintage GM cars are round, and a 5x7 fits fine. But why the convertible designation? Calling them,, they say that some Cadillacs use a 6x9. But which ones?

I don't have an original Delco manual for this car. However I have Sams book AR-10, which shows a 6x9 for the rear -- all models.

So which is it? Do the sedans/coupes take a 6x9 and a convertible use a smaller one? Does anyone have a factory book that spells it out? What about the 1960-66? Same thing?

If anyone has information on this, it would be greatly appreciated. Thanks!