My guess ( and it is only a guess, as i have not done this) is that the engine/tranny will sway in fairly easily. After all that engine and tranny was offered in the 300SD. The chassis for 2 cars is the same except for the extra length in the SDL.
Use the motor mounts from the 300SD, and probably the cross member from the 300SD. You may have to play with the length of the driveshaft. I doubt that either would fit w/o modification.
You may want the rear end from the 300SD, too. Check if they have the same ratio. You might want the lower gear set ( higher numerical) if they are different. That 3.0 liter may be a little under power for the longer chassis.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags