If they just bolted the 240 flywheel to the 300 and made no effort to statically balance the 240 and 300 flywheels, then you should not be surprised by vibration.

Same if the driveshaft sections were taken apart and not marked.

I have never been able to figure out the real story on transmission position with different engines. I THINK that they keep the rear of the engine in the same place and vary stuff like the water pump shaft length.

I would be interested in other knowledge or opinions.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe