Thing 2 helped me get the chuck apart tonight.
There were two holes in the bottom half that I missed in all the paint and gunk. We dug through the bolt can and put a couple in his little bench vise that lined up with the holes in the chuck. We set the chuck on the bolts, wrapped the upper half with a scrap piece of leather, and used a pair of channel locks to break it loose. All of this was so we could dry, wire wheel, oil, and reassemble.