I have option D on my recumbent and would not suggest using such a small threadless adapter - too much leverage if you ever push or pull on the handlebars.
However, all may not be lost. RANS does sell a
longer threadless adapter that you should use, and you'll also have to buy the
post clamps as well. Should your stem be too wide, you might have to pick up the shim as well. Just cut the stem to size, and read
this article with care about modifying the stem.
RANS' quality is pretty first rate, so no worries there.