I dont know for shure about the weight but I can tell you with certainty that a 300D motor and trans is heavier, A LOT heavier than a 5.7 GM motor with t56 trans.

I have pulled both motors with an engine hoist and you can FEEL the weight of the motor on the hoist with the 300D. The hoist's struckture was creaking and bending, it was pretty scary.

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1985 300D : the clean one 180k miles - Now passed onto my parents.
2000 E39 M5
2002 e46 330xit
1991 mustang notch (project)
1970 chevelle (project)