For a few bucks, at the Rebuilding Center, I was able to fabricate this thing.
Now, I was hoping to build in more adjustable parts, but I could not get everything to work.
The lower shelf has wooden brackets that connect to the main verticals (2x4's). These brackets were supposed to have holes drilled in them which were going to correspond to holes in the verticals, but that was easier said than done. For now, the shelf is "pinned" to the vertical members with screws. On a large painting, it is unlikely that I will be wanting to move it up and down much. It only takes a few minutes to reset the screws anyway.
If this works out, maybe I will build a more refined easel for this purpose.
In any case, I can now make paintings up to 80" tall if I want.
The photo was taken with my new camera, a Nikon Coolpix S3100. I sold a painting and invested a little in this new camera and am already enjoying the quality of the photos.