What do you mean by "received"? Are you talking about having someone send it to you? Your question is vague and confusing. It would help to answer if you were a little more specific.
For an AK or AR... If it has the lower receiver (the part with the safety attached) it requires an FFL "receive" it for you if someone is shipping it to you. If there's no lower receiver you don't have a firearm so it could then be shipped right to you.
Obviously if it's a face to face in OK it doesn't matter.
Must go to an FFL. A stock, upper receiver (for most guns), barrel...none of that has any bearing on whether or not it must be received by a licensed dealer. Only the lower receiver matters (again...for most guns). If it has a lower receiver, completely assembled or not, it's a firearm and can only be shipped to a dealer.