I have been offered a free '80 300SD... of course, it is FREE because the body is a wreck and it has been sitting w/o use for several years (i.e. there are now raspbery bushes growing on it!). I have been told the engine ran well when it was last used (has 240k). I'm going to do some more checking into the engine in the next few days.

I also know a guy who has an '85 300 with a manual transmission. The engine is shot and the rear end is pretty smashed in, but otherwise the car is beautiful.

Here are my questions... what is the likelihood that I can take the rear of the '80 (which is still in good shape) and its engine and replace it on the '85? Compatible or no?

The rear of the 1980 car is a W116 chassis & the 1985 is a W123 chassis!
UNLESS you are the best custom body man in the world then that wont fit!

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Considering the W116 is about 6 inches wider..............

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

How about engine compatability... many modifications?

Engine will swap...but you need to use the right engine mount pedistals off the block for the body you use. Those are different between the W123 and the W116

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

This is what they make salvage yards for. The price of the car is going to have to be WAY better than free for the project to be economically viable.