you souldnt have to cut anything... the cat back should be a bolt on... it bolts off at the dne of the h pipe which contains your cats...... then just bolt the new one back on... the bolts are either 13mm or 1/2 i think there is 2 on each pipe
maybe if the bolts are rusted over... mine were hard to get off... spray them with liquid wrench a day b4... and it should be fine... i also bought new ones to put back in