Radio conundrum solved. My interior has been redone so I didn't want to chop holes for speakers. The radio panel had a cassette player which didnt work.
So I installed a more modern device (all black ) and, for stereo, put two 4" speakers in behind the panel with some black speaker cloth.
The headache was making a plywood piece for behind the panel with two speaker cutouts, had to accomodate the heater sliders and couldnt drill through the retrimmed panel front.(had to just use the openings that were there).
It looks quite nice and is stereo.

 

in the S type and 420, there are 8" inch round cutouts, one on each kick panel, ( driver and passenger sides), behind the upholstered cardboard kick panel. They are closed with round metal covers each with four 8mm bolts from the factory.

I found they are a perfect fit for Clarion 7.5" inch round Marine speakers. The opening is like a hollow speaker cabinet between the inside kick panel and the outside wing, allowing incredible Bass resonance.

Does the MK-2 have those cutouts ?

 

Jose - Yes, the holes and covers are certainly there on the Mk2. I assume they're the same size.
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Thanks Peter. I wonder why the factory added them and then covered them. Access to installing an antenna for sure, but never mentioned in Shop manuals as suitable for speakers.

 

An idea hole during a restoration to spray copious amounts of Waxoyl into the void of the front wing and the front of the sill section to protect from rust..