Gregg,
You mentioned "speakers are lousy".
What size are they and where are they located? I noticed you have a speaker grill on top of the dash. My '72 250C still has the factory Blaupunkt stereo radio with a single'
4"x 8" speaker in the dash and one matching
4"x 8" speaker in the rear deck. They still sound far superior to the four speaker, Becker system that came in my '72 250 sedan, though not quite as good as a modern stereo.
actually, A good factory speaker in your dash might improve things, if there's not one there already. A good sounding radio installation is an art I haven't quite mastered yet. The radio installation in my 220S is still a 'work in progress'. I have 3 original, mono radios that will fit in my dash (I'd rather hear a good mono radio than a lousy stereo) but, without hacking holes in my interior, trying to fit a decent sounding speaker has been frustrating. Unfortunately, the '60 Finback cars had no factory dash opening for a speaker.

Happy Motoring, Mark

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DrDKW