Alright now this one I know I can answer since I have to learn this as a Ford Technician. A 50 state legal catalytic converter catalyst is designed to pass the most stringent emissions tests of California. Where the 49 state legal one doesn't have that high a level of a catalyst. The difference you will find when you try to get one from Magnaflow is that if your car came from the factory equipped with a California catalytic converter and you order a 49 you will get a MIL which no matter what state you live in you will fail emissions testing. Magnaflow actually has a code for the engines that you can get from your car that tells them what the type of catalytic converter your car comes equipped with. Here is a perfect example of why this doesn't matter what state you're in but how your car came out of the factory, I live in Pennsylvania and I purchased my car in a county that doesn't do emissions testing due to our population density and my car is equipped with a California 50 state catalytic converter.
Infra-Red SVT ZX3