I like the insurance policy of having the nut on the bottom. That way, gravity works in my favor in the event of a failure.
Also, I can't imagine getting a torque wrench on the nut if it's on top, so it is unlikely it could be torqued accurately upside-down.
Manipulating the engine position did not work well for me.
Removing the rear exhaust manifold was really not that bad.
1986 300E 5-Speed 240k mi.