The main item is the HB-1 pickups manufactured in 1988 will be closer in tone to the origionals. The later HB-1 are a little different in tone. The later ones seem to have a pinch more distortion and a little less kick. However this is not based on engineering measurements of the tone or composition of th epickup.
The other difference is the pickguard is likely clear with a black paint backing + gold Guild wording and is mounted with the pickguard clear of the pickup bezel. The early X170's have a black-white-black-white-black laminated pickguard andit overlaps the pickup bezel. Some players don't like the overlap sesign because if it "slaps" the bezel the slap can be amplified by the pickup.
An '88 X170 will likely have a 1 5/8" neck while the 2001 will have a 1 11/16" (at the nut).
Pickups on the '88 will be worlds better than on a '01 IMO, assuming they haven't been replaced.
The pick guard mounting over the rings drives me nuts because it interferes with my picking at times. That or I don't like the way it feels while I'm playing. I can't remember which, but I know I don't like the design for tactile reasons.