Well the rear bulb burned out on the second ride. I ordered some bulbs from Bulb Town and currently have a
#1447 (18 V, .15 A) bulb in there. The headlight seems the same, the tail light doesn't glow quite as bright (a good thing I think; I suspect the other bulbs were over-stressed). So far, so good. If it burns out quickly, I got some bulbs that run on even higher voltages (but draw a little more current).