Deejay's description sounds as if the bolt that screws in from the bottom is indeed a yard long and screws into the crankshaft. If so, the upper pulley can be removed with a gear puller provided you screw the long bolt in first, and apply the screw of the gear puller to the head of that bolt, not the end of the shaft extension. That approach is better than the slide-hammer, which applies impact loads to the crankshaft thrust bearing and the side of the crankcase.
It also sounds as if the aluminium adhering to the crankshaft extension is there because of corrosion and seizure between the aluminium and steel parts, not because the aluminium part was running loose. Let's hope that was the case, since the aluminium part is expensive to replace. When you reassemble, you should put some suitable lubricating agent on the crankshaft extension so the corrosion will not happen again.
