Nearly every AR-15 manufacturers: DPMS, Olympia, Bushmaster, Colt etc etc do not ship parts to California.
You never need to have a FFL license. This is a license to run a gun shop. That would be the same as buying a Ford Dealership instead of an Escort to commute to work.
In California - barrels that are threaded, have a bayonette lug, etc etc are illegal. If your upper is 'street legal' in California there is nothing wrong selling it - they are just parts - not a complete rifle.
Hope this helps