I really advise against using the cam sprocket. The torque here is above and beyond this. Something will break. You need to brace the crank itself.
I have not worked on your engine. I wonder what the factory tool for this looks like? Do you have a manual? Sometimes the factory tools stop things on the pulley end.
They make a special general automotive tool that locks onto the flywheel, often positioned where the starter goes. This sort of 'flywheel lock' tool is pretty widely available.
What would it take to drop the pan? Wedging the crank against the block (with a scrap of wood) has never failed me.
1986 300E 5-Speed 240k mi.