Yes it's a direct fit.
The 89-93s varied in side trim and some GFX kits made for them will extend all the way up to the side moldings for a seamless fit:
-89-90s all had thick black painted side moldings, same thickness as the "bulge" on the front/rear bumpers
-91 carried over the same front/rear bumpers but body colored the section below the trim inserts, but the side moldings were changed to thin strips, to match the thinner black/trim area of the fronts(similar in thickness to 89-93 SC moldings for that matter)
-92 carried over the 91 trim for the BASE models, but body colored everything but the inserts, and LX and Sport models got the SC front bumper and tapered side moldings, lifted from 1991 Cougar XR7, which are thin at the front and thick at the rear(as thick as the rear bumper bulge). Rear bumpers were carried over for all models
-93 was consolidated into a single LX package, and the front SC bumper and tapered side moldings were exactly like the 92 LX and Sport. The only difference being the chrome trim inserts in the quarter panel moldings and rear bumper cover were deleted and smoothed over, but the shapes themselves were identical.
So if you have a GFX kit meant for 1993, and this kit has extensions up to the moldings/bulges, your existing rear bumper will work with them, since the only difference in bumpers are the trim inserts. The side moldings would be where you'd run into issues, because there'd be a gap between the GFX extensions and your thin 91 moldings.
If the kit you have only covers the rocker panels though, then it's a non issue, only difference would be the front bumper.