You can place a block of wood between the crank and the engine block to stop the rotation, then use a big breaker bar with a pipe on it.

This method has never failed me.

Obviously, the socket and breaker bar have to be up to the task.
A number of sockets haved failed this particular test...

I have personally had no luck with pneumatic tools here, and wonder about the 'beating' that the percussion places on the rod bearings (if they are still in place)...

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1986 300E 5-Speed 240k mi.