Welcome! I'm Ron Z! I will do my best to answer all of your questions. For easy access to this thread, bookmark it now! Please read everything!
What year is this Chevy?
Ok, the P0449 is fairly straight forward, pointing to the Vent Solenoid. The solenoid is located under the vehicle, towards the rearmost of the vehicle, mounted to the EVAP canister. Carefully inspect all the vacuum lines and tubing in this area for any cracks, holes or loose/missing connections. Inspect the electrical connector for any loose, broken or rubbed through wires. If the visual inspection checks ok, replacing the solenoid should solve the problem.
I found several numbers on line XXX-XXXX XXX-XXXX XXX-XXXX
I'm in the GM parts catalogue, and there isn't one listed, so I cannot confirm any numbers you found online. Those part numbers you listed look like after-market part numbers. GM part numbers in the evap system are usually 8-digits. Those look like, maybe... "Dorman" part numbers? I wouldn't trust it. Get the GM original.