On my sd's I had to beat the firewall in to clear the o2. On a set of ssac's I installed the crossover didn't line up.
so what did you wind up doing for the crossover? and when did you install? is there a chance they redesigned? i don't imagine the setup in the 98 and 01 is too different as far as space and exhuast are concerned. but maybe
2001 GTP Special Edition
ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....