I'm going from the stock 4 cat h pipe set up to a magnaflow with just 2 cats. Does the stock 4 cat system have 4 02 sensors or only 2? Will I get any codes from this change? The car is a stock 89GT. And if anyone has the part number or link to a 4 cat magnaflow h pipe send it my way, I've only been able to find their 4 cat X pipe. Thanks.