You got to get over the idea that anyone would EVER go back and redo the special effects for this film. Accept the Assembly Cut for what it is Local. The 2003 version is the closest thing we will ever get to, "updated special effects".
They did actually use some CGI to finish off an unfinished effect shot especially for the AC. Specifically, the shot of the infant Alien running away from the ox. The creature legitimately is CGI in that shot, and it was done in 2003.
it was all a dream.
I thought the dumb dream idea had died.
ah, so it's like the Director's Cut?
It's the same thing; the extended version is officially called the Assembly Cut, not Director's Cut, because the director had nothing to do with putting it together (short of his original notes being used as a guide).