[Fitz Frobozz]

Option #3 did the trick. Seems there may be quirks/issues that disrupt vertical alignment for elements that are inside floated elements (or are floated themselves, as I was seeing the other day). In any case, thanks for taking the time and being so helpful!

This is what I ended up with, which aligns left- and right-hand columns to the left and to the right, and both columns to the top:

  <div class="top-outer-left">
    <div class="top-inner-left">
      Lorem ipsum: <em>dolor sit amet</em><br/>

      Ut enim ad minim veniam: 1234
    </div>
  </div>

  <div class="top-outer-right">
    <div class="top-inner-right">
      Duis aute irure dolor: 5678 (Excepteur sint occaecat)
    </div>
  </div>

.top-outer-left, .top-outer-right {
  width: 49%;
  display: inline-block;
  vertical-align: top;
  font-size:.85em;
}

.top-outer-left {
  text-align:left;
}

.top-outer-right { 
  text-align:right;
}

.top-inner-left, .top-inner-right {
  margin: 0;
}