My only hesitation with that rig is not the size of the base, rather it's the short column. You can always drape a publication over the sides of the base, but without a taller column you'll be forced to use ever-wider lenses and could run into distortion issues. I can't tell how the camera mount is attached to the column, but I'd seriously consider replacing the column with a longer one. We've got a large commercial stand (24x30"), but I'm happier with one I made myself. I just attached a piece of hardware called a "floor flange" to a piece of plywood the same size, but picked the particular floor flange because it mounted a pipe the same diameter as that on the commercial stand. When I need a longer column, I just transfer the hardware from the commercial stand onto the (longer) pipe mounted on the floor flange. Simple solution for you too, if in fact the mounting hardware on that little stand would allow you to install a longer column as needed.
Thank you Hank, your thoughts are very germane. However, I have two parameters I should have included in my original post:
1. The stand has to be portable by disassembly and carriage in a cloth bag, since I will be carrying it in taxis and on planes. This implies light weight.
2. The copies I need to make are for textual reference, not archival photography. As long as I can read the resulting JPGs, they will be OK.
I did some tests with my digicam held at 12" above a couple of books & mags, and the images were fine at ISO 200 by ambient lighting. I can always go up in ISO if the archive in question is not lit brightly enough. I saw some folks at the National Archives using ambient light and snapping away all day, so I think this will work.
I called the vendor of the stand I linked to and it is out of stock until later in December; I need a stand before then. So I think I shall make one of baltic birch plywood and some cheap mounting hardware I found on Amazon.