hi there, the rear arches and valance will fit as the rear of the shell was the same externaly however you will need to relocate the reverse light if you fit the valance as the mk2 had them in the light clusters rather than below the bumper, but im afraid the front arches and splitter wont fit as the mk2 front end was completely revised making an inch or so more room at the front of the engine bay in the mk2,
if you are looking for something a bit larger than the mk1 xr kit have you concidered the old MC rallying kit, originals are no longer available new but various companies do copies of them cheap