I don't know about this specific car, but can offer generalities. Also, how long does the owner want to keep car? If a trade in is looming, don't do much other than getting it running. Don't bother trading in as is,a car dealer won't give much for a non running car ( ~ $ 500 actual but they might claim they are giving $ 2,000 + )

If auto trans it should be a 722.6, nothing special to split the two.

If 4 matic the oil pan will likely be different.

Change the crank sensor, they are usually in a difficult spot on the rear of engine.

Change any hard to get to coolant hoses, water pump, belt, maybe valve cover gaskets if leak prone. Maybe an upper hose.

Crank seal could be changed with proper tools, I would not do anything with the trans.

Usually it is easier to leave the wiring harness on the engine and unplug from car.

Try the nation wide salvage yard inventory search car-part.com for a motor.