hi I have been given a sportex race tube as a belated birthday gift from my son as the middle section of exhaust is knackered and I have a couple of questions regarding the fitting..firstly the tube is 2.5" in diameter and looks huge does anyone know if it fits the standard cat and back box?both of these are in good condition and dont need to be changed..secondly after having a quick look underneath I noticed the studs that are part of the cat that the tube will connect to look pretty nasty are they part of the cat and if I should break one will it need to be drilled out or are they nuts and bolts. Im hoping they look worse than they are and a good wire brush and plenty of wd40 will help.any tips will be appreciated.