You could, I'm sure it's been done. The issue is that the pumps aren't governed off of idle so you'll need some sort of goveber to get it to run at a constant speed under load.

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2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Very true.

Even ignoring governor issues, the engine would be hugely outsized compared to the generator I'm looking at. Wouldn't be long for this world, being run so lightly loaded.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

I recently bought a 300SD to pull the OM617 out so I can put it in my '87 Nissan D21.

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2010 Mercedes E350 4Matic - 77k miles
1986.5 Nissan D21 V6 4x4 - 276k miles
1987 Mercedes 190D 2.5 Turbo - 3??k miles
1983 Mercedes 300SD turbo parts car
2017 Honda CBR500R - 15k miles
2016 Suzuki GSX S1000 - 9k miles

Mercedes put the OM616 into the Unimog 421's, not much speed out of them, but lots of grunt work could be done.

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Von
Fairport, NY
1973 Unimog 416 Doka
1980 Unimog 416 Doka
1981 Unimog 416 Doka
1984 Euro 280CE w/diesel conversion
1985 300TD Estate wagon
(I really need to stop buying these things!)
http://vonsmog.com