So after 21 years my catalytic converter has fallen to pieces. Looked up the replacements and according to the CARB website (https://ssl.arb.ca.gov/AftermarketParts/catalysts) and literally every cat has an inlet and outlet of between 2.25 and 2.5 inches.

Now, I measured my exhaust. The down pipes from each manifold are 2.5 inches. They merge into a Y and transitions into a 3 inch which is what the factory cat is. 3 inch in and out.

I ordered a 3 inch CARB cat on Amazon but now i'm concerned it wont pass because the EO number for it is for a chevy. The applicable cats for mine are all 2.5.. so what, I need to neck down from 3 inch, to 2.5, then back up to 3 inch for the rest of my exhaust?

Anyone ever gone through this before?