In your case, you know where to look for a resolution as the Bing floats were the last service you did. Some of us ain't that lucky!
As the engine shut down completely, that makes me wonder if there was any fuel being drawn into the carbs. Often, one jug will quit and you limp home on one cylinder but this is not the case
Pull the bowls, turn on the fuel tap - you did turn on the gas before the test ride? - and note if fuel passes. Raise the float and confirm it shuts off fuel, then drop the float again. Confirm that the gaskets have not interfered with the float ops. Check both float needles for freedom of movement. Are the needles correctly fitted to the small wire bales?
You might pull the spark plugs and dribble in a little prime gas. If the engine starts up and briefly runs, than you'll pretty well confirm there's something amiss with the carbs.
Both side quit running? That's a new one.