I have a 2000 Discovery 2 with secondary air injection could I put an engine without secondary air injection and still be able to pass U.S. emissions and drive the car right

 

Depends on your state's laws.
If you don't change the ecu, bcu, dash to those from a non sai truck, you're going to get a check engine light, which will fail in most states.
If your state has the tailpipe sniffer(not all do)again depending on that state law, it will likely fail, but may pass based on it's age.
Also, strangely enough, the tailpipe sniffer is not required in all areas of the same state to pass inspection.
Here in Va it's the same standard test state wide, but the tailpipe sniffer is only done in the Northern Va area and not required elsewhere.
What state are you in?

 

Also, the only engine difference is if the heads have the sai ports or not.