Looks to me like a W126 300SD. SDL's weren't made in '84, but somebody might correct me.

I'd suggest this one over a W123, but than again, it's really just a different option. Same drivetrain. The gearing in the transmission may be a little different. W126 have a different frame design which helps cut down the weight of the vehicle compared to it's size. You'll have some resonance from the hollow frame vs the W123. Those are really minor things.

Others may point out other details.

The larger body size is nice, yet I really prefer my W123 going around town, it maneuvers a little more flexible, parking lots etc.

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