Why is a solid backing needed behind a pedestal sink? The pedestal does
support it, doesn't it?

In any event, I'm planning to install one that I found--at a time when I
was considering buying one--that had been left at the curb in great
condition. It's a Glacier Bay model. Of course, I have no installation
instructions, no measurement guide, no drilling pattern. Any tips about
making sure I fasten the sink to the wall at just the right location?

Also, I'm not sure what kind of fasteners to use. One of the old ones
was still stuck into the hole in the back of the sink--it's got a
metallic anchor that runs most of the length of the bolt. I'm not sure
how that works with drywall with a wood plank behind it--I thought
anchors were for drywall-only attachment.