Had no luck with Arthur's method myself, but you never know...
I think this thing was designed to be removable before the pre-cats were tacked on there. Bet they do not have this issue in some other nations...
I should mention that removing the manifold went smoothly both times. Perhaps I was just lucky, but nothing froze or broke at the head or the headpipes.
If you do go this route, it would be ideal to have a new manifold gasket on hand.
The first time, I was able to clean the old gasket up, and get a good seal. I applied a bit of Permatex Copper gasket maker as insurance.
The second time, I ordered up a new gasket in advance.
1986 300E 5-Speed 240k mi.