OK. When I started working on the transfer last night, even the "B" pencil wasn't "enough" (wasn't thick enough, or soft enough) to transfer well.
So, I went over the drawing again with charcoal pencil (I used about eight of them, since they're only sharp enough to make about a ten inch line before getting dull, and I didn't ant to spend all evening sharpening and re-sharpening pencils).
The panel was primed with two coats of Liquitex acrylic gesso (sanded between coats) followed by three coats of Gamblin's "Traditional Gesso" (also sanded between coats). This is the smoothest, nicest surface for drawing and painting that I've found (or been able to create, myself).
That worked well, and the drawing is now transferred to the panel, and I'm going over the drawing--yet again--and making it sharper, and adding more detail.