If a car dosent have factory catalytic converter (not because its missing, but because it wasnt designed with one) and you do a swap for a newer models engine, do you have to put in cats even tho there is no stock one for the year of the vehicle? are the stock cats from the new motor considered a "factory replacement part"?

Eny insight would be helpful
-thanks

Yes, body or engine, which ever is newer is the one you must conform too.

In PHX AZ (Maricopa county), you have to build to the VIN year of the vehicle. If your vehicle did not come from the factory w/ a set of cats, then you don't need them. Whatever emissions came on the vehicle per that year have to be on and functioning at the time of yearly inspection. Your local "area having jurisdiction" may and probably is different.

You should be able to find your answer here. http://www.epa.gov/
I've run into this trouble before. While local laws may allow it, I gaurantee the EPA does not. I used to own an exhaust shop and attended many EPA meeting on emmision law an they have jurisdiction nationwide.