Yeh...I have a similar situation:

Dad bought a 1993 S350 140 Body with typical signs of Rodbender. Recently I found a 1987 300D with a good engine but rusted body for cheap. In the big picture, I can swap the engines. Sell parts from the 3.5 and recoup quite a bit. The #17 will more than cover the cost of my entire parts car, but I will most likely keep it for MY wagon with the #14 head.

I will say however, the W140 body is complex. Intimidating for me at least. Even with a good running engine, unless everything else was perfect, I would be weary. The luxury items will nickel and dime one to death...

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1987 300TDT - 195,000 (Original #14 head)
1993 190E 2.3 - 105,000
1981 300D - 250,000