Can i replace my exhaust manifold and O2 sensor with Fed parts after Cali parts?

Hello RKLINGER.1214,

Depending on where you live in Oregon you may be exempt from emissions testing. Some vehicles are exempt from emission testing if they are 20 years older or more. In Oregon, if you live in a metro area, you will need to get emissions testing every 2 years. Other parts of the states are a little more lenient on these laws.

Check with local government to make sure your vehicle follows the laws in your area.

Here is a link to some more information:
https://www.dmv.org/or-oregon/smog-check.php

Also, a lot of states have adopted California Air Resources Board or CARB emissions standards. Oregon is one of those states.

With that the federal government has laws prohibiting changes in emissions systems.

If your vehicle does not meet emission standards in your state, you may have to replace the parts and you may even get fined.

Here is a link with some more information:
https://www.carparts.com/blog/federal-vs-california-emissions-what-you-need-to-know/

In the end, you should always replace parts on your vehicle with ones that your vehicle came with. Otherwise, not only could you have issues with emissions, but the vehicle may not function properly.

Hope this helps.

Thank you,
Brendon