I suspect that the challenge would not be so much shoehorning the engine into the chassis (although others may have a better idea how much longer the 6-cylinder 603 block is ) but rather in finding and installing all of the bits and pieces that make up the "EDS" (Electronic Diesel System). A late (say, 1984) 617 engine might in the long run be a better choice for a workable installation....

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970