Okay, got it working. I discovered one other problem with the mix-n-match headset I was trying to use yesterday. Instead of mostly NR and one or two SR bits, it was mostly SR and just one NR bit, the lower cup. That reduced the stack height of the headset enough to keep it from working. When I found the proper SR cup, things worked with the three spacers I was using yesterday. (I don't have a real SR spacer. It will probably not be enough, but should only require one extra spacer.) Though this isn't likely to be the last iteration, it will at least allow me to finish putting the bike together so I can explore stem/handlebar combinations. Thanks again for the inputs.