The core support does not have to be switched. If you notice the two metal tabs with holes in them on the front of the core support, the bumper is attached there with two plastic push pin. bout 3/8 inch wide. If you notch those with a die grinded and re drill new holes. Your 99-00 bumper will fit.! DO NOT CHANGE THE CORE SUPPPORT. If welded in wrong.....well your asking for a list of issues