The speakers in my 750L are in the rear trim cards, while the speakers in my 45CL are mounted in the sides of the plastic door pockets.
Both have got their original 'Sparkomatic' speakers that were fitted when new. They're a load of crap but I can't be bothered changing them as they are original.
Is also common, as suggested to put in the front, probably easier too.
My 45 CL also has it's original 'Sparkomatic California' Radio/Cassette :worship: It still works, but the quality is appalling and it only picks up Radio 2, but it's original so it's staying. It's mounted in a Fiat holder that fits between the door and the steering column.