The assembly cut is on the Alien Quadrilogy. It's Alien 3's equivalent to the Aliens special edition... Though in Alien 3's case(At least on the original DVD quad release) it has unfinished sound and some additional sketchy effects. It restores entire subplots that were cut form the movie. IE the prisoner's seal Spike in the trap after the explosion, and then Golic is untied and goes and releases Spike from the Waste Containment, only to get shanked by the alien for his trouble. There's other bits and pieces all over. The entire beginning is completely different with Ripley washing ashore. The burster comes out of an Ox instead of a dog... etc etc.