Interesting you should mention this, as it is a project I have sitting in the garage right now.


I actually bought a vehicle someone had done this exact modification to. They used the original drive train Swapped out the ends of the transmission (held on by a large nut).
Everything swapped over very easily. They used a 6.9 Radiator and oil cooler in place of the 78-80 oil cooler and radiator. And they spliced the ac line to power the glow plug relay, while removing the ac compressor (the ac switch became the way to turn on the glow plug unit, hold for as long as needed). They also swapped out the instrument cluster and fed the oil line into the dash.


It is a really clean and straightforward swap. The chassis is just over 4inches longer and everything else on the w116 chassis are the same.


As a side note bc I was concerned about the weight. The 450SEl and 300SD weight the exact same, assuming you swap the aluminum deck and bonnet over.


I drove the car over 500miles back from ohio, handle the same, drove great. Didn't notice much difference being 4inches longer. For a passenger though, what a world of difference.

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