Noise Problem Solved!
I figured out the source of the clonky, thwacky noise on my 1952 Superbe Sport Tourist. I had only been checking the bottom bracket by pulling on the cranks to see if there was play. I decided this morning, that, in spite of there not feeling like there was any play, I would readjust the bottom bracket bearing. When I went to loosen the lock ring, I found it was already very loose. I tightened up the lock ring and the noise disappeared. What a relief. I didn't want to tear the hub down again.
It was actually a good thing, because I found a lot of other things that had loosened up in the year and a half I've been riding the bike. The little bolts holding the section of the chainguard underneath the rear cog were especially loose, but everything I tightened up needed it.