Yes. "280" was the number of the inspector assigned to that factory at that time. Actually, he was the head of an inspection team; though he was primarily an administrator, he was responsible for quality control for the products that factory made for the army. With one or two exceptions, the actual names of those men is not known; it was considered secret. The papers were apparently lost and the men involved kept the trust.
The three marks are final inspection of the receiver, final inspection of the barreled action, and final inspection of the completed rifle. The larger eagle is the proof mark.
Jim