On the A-body convertibles they started out by putting speakers at the base of the well liner for '65 (bad idea, all debris falls into it and bounces in the cone). It was revised for '66 and continued into the 70s with a wedge-shaped speaker box on the back of the seat near the top, inside the well. It was aimed towards the back window and beat Bose in reflected sound technology. Accidentally.

That 1968 Parisienne sounds like it might have one of those wedge shaped boxes under the vinyl well liner, capped with a speaker grille on the outside. It is likely more weather-resistant that way.
I would expect the speaker to be a 6x9 10 ohm model. The wrong impedance speaker can blow the radio after a bit of use.

seventy2plus2 wrote:

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I wonder if a 68 Canadian Pontiac Assembly Manual would show the convertible rear speaker setup.

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 If only we knew someone who has that manual.... 

I'll try to check tomorrow.

seventy2plus2 wrote:

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One of our members bought a 68 Parisienne convertible in summer of 2023.  I saw it had the fader, but never thought to see where the rear speaker was.

He sent me this photo and description:

"Right rear, attached to vinyl cover that goes down back of rear seat.

It appears to have a hard cover around the speaker inside of the vinyl."

I have one of those grilles, and likely saw one of the hard covers the speaker sits in at one time but didn't realize what it was.  The speaker would be 10 ohms, I presume 6" x 9".

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 This speaker box must be mounted above the convertible motor I presume. Definitely be nice to see the other side of the grill. Would Impala use the same system? And Clint. Id be interested in that grill you have if you want to part with it. 

Thanks Clint.

Not sure if these are what you are looking for, but they are made to original specs. Speaker Enclosure for 1967-68 Chevrolet Fullsize Convertible CVY-RSE-110