SCO develops and supports SCO Unix, they are the modern incarnate of the original SCO, certainly the closest thing. And SCO Unix was the original Unix for PC's, it's too bad IBM dropped the ball on making it better, and left everyone with Linux and all these leftists and IP issues instead.
1987: The year that Xenix (what SCO Unix was at the time) was ported to the x86, and the year that Minix was written for the x86. In other words, it's about a tie. But I'd say Minix is the original x86 UNIX since it was actually written for the x86, not ported to it.