If you can cram W140 wheels onto your 350 you’d have the equivalent of going from your 2.65 diff to ~2.5. With the standard W126 tire size, a 722.6’s 0.83 5th drops you to an effective 2.2, or 2.0 with a 722.5’s 0.75 5th. Either is way too low unless you cruise at over 80mph.

Math class was a while ago so I hope these numbers are correct.

Sixto
98 E320s sedan and wagon
02 C320 wagon