Don’t know what other state laws are, but in Texas it is illegal to sell a vehicle on which the emissions systems have been modified. Keep the parts. You may have to reinstall to legally sell it.
Texas law prohibits any person from selling, offering for sale, leasing, or offering to lease any vehicle not equipped with all emission control systems or devices in good operable condition. Violators are subject to penalties under the Texas Clean Air Act of up to $25,000 per violation. Buyers are advised to have the vehicle checked for all required emission control devices prior to purchasing a new or used vehicle.