Al,
You made it clear from the start that the top mount is loose, all tension is removed and the bolt turns freely but won't slide out of the lower mount. I'm wondering if the bolt has worn a "notch" over time, like perhaps the lower shock end has now dropped down some amount into a wide groove, forming a lip that's holding the bolt? Can you perhaps lever the bottom of the shock up as you turn the bolt, and try to tap it out of place? It may take another pair of hands to do all of that at once. If it's not eroded into a step, I'd say cutting it out is the only thing left, like Mike suggests.