I have an 84 K5 and swaped out my old 350 for a 94 LT1 engine. It's up and running and I have all of the exhaust in order but want to know what to do about my cat? I have a cat from a 1995 Camaro that was the same as the donor car but the cat I have now is a 3 inch one that would fit my system much better. Would it be alright just to keep my old one. How different are cats for different makes of vehicles?