Catalytic Converters

2002 Ford Mustang GT, 4.6L, V8, 69,000 miles. I bought this car used at a used car dealership with a good reputation (Car Max) in NV in 2004. They said it had custom fabricated racing pipes. I smogged it upon moving to CA in November and it passed no problem. However I am trying to sell my car and it needs to smog again within 90 days of me selling it. I took it to a dealership that said they would pay me blue book for it. When I got there they looked at it and said they would only give me about half of what the blue book was because it needed a new exhaust system because it was missing catalytic converters which is illegal in CA. They said who ever smogged it smogged it illlegally and it woudn't pass the visual inspection. I then took it to a mechanic to check out and they said it was missing only two cats but has four and is supposed to have six. They said they would charge me about $1200 to fix it because they would need to put on all new head pipes due to the type of exhaust. I don't know what this means. My ex who bought the car with me and drove it before my move to CA said just to get two three chamber flow masters and have someone else put them on and it would be much cheaper. I can't find flowmasters catalytic converters anywhere online, just mufflers. My ex also said it doesn't need six cats, it is legal as long as it has one on each side. I don't know who is right or who to believe. Please help.