I've tried searching but couldn't really find a direct answer, i currently have a 3" down pipe, witch connects to a y-pipe, 4 bolt pattern. I was sold the car with the cat but with no y-pipe and mufflers. I was wondering what kind of options do i have to temporarily put on the stock, 2 studded cat to my aftermarket y-pipe to pass emissions.

 

either eliminate the flanges or have custom flanges made so that they mate.