For the benefit of future readers, here's how it went.

Our KE A380 arrived from Incheon a minute or two early. We were disembarking at 8:45 on the nose, Gate 26 at NRT Terminal 1, IIRC. Prestige Class was basically empty, so it was a quick disembarkation, though we were in the midst of Economy pax from the Lower Deck by the time we hit the terminal.

We walked quickly to arrivals. Immigration was totally empty, so we walked right up to the desks. Baggage claim was similarly empty, just one or two flights, though my companion dillydallied a bit, costing us a few minutes. Our priority-tagged bags came up pretty quickly. We walked straight to a Customs inspector, who questioned us about the wine we declared and opened one of our bags for a paw-through (in typically polite Japanese style). Using one of Narita's escalator-friendly baggage carts, we circled down into the train station, bought tickets for the SkyLiner, and dashed to catch the train. Two minutes later, the train eased out of the station.

We caught the 9:08 pm departure!

We transferred at Nippori, thanks to tips in this thread. It was fairly easy. At that hour, the Yamanote Line was fine. We alighted at Yurakucho, walked a few blocks to our hotel. We were in the room by 10:20 pm.

Thank you, FlyerTalk.