sorry bout the sketch :roll:
so those old stems have a split on the bottom. and a wedge thats driven in to the middle.
when there reefed on, they often flare the fork tupe as well (2nd doodle)
thats probably what your dealing with.
now even though the wedge let loose it could be the wedge is still in place (ie the bolt snaps just above the wedge) if you dont remove it, your task will be impossible (or next too)
now if your bolt did snap above the wedge (which it usually does) that bolt won't be long enough to remove the wedge.
remove the bolt, take a metal dowel/really long screw driver and ensure that wedge is removed (hammer down through the bolt hole, when it lets loose it will just fall to the bottom of the fork tube.)
the rest is just a battle of will.
you gotta pull hard enough to force the stem through the fork tube compressing the flared end back to its original diameter.
i assure you, it won't be easy, but it is do'able.
i'd be willing to bet cash, this is the case with your ccm (ontop of the corrosion)