So I had a look at the parts I had tonight. Four steppers, three with screw attached. Three plastic lead screws, a Print5D D8 printer controller, a bunch of screws and metal rods, and a 3D printer.
I've been amazed that the Lulzbot has so many 3D printed parts - this makes me far more confident that printed parts will hold up strength wise for what I need.
I think I'll rip off the Z-axis design of using two steppers and screws for the X axis. That will need to be able to drive the Y-axis reliably, so having two motors doing that work sounds like a good idea.
I have two motors and screws that are almost the same size, and two matching plastic lead screws. If I take out the metal rods that are and use the two larger rods to join them together, I'll get little gantry system going.
It looks like it might work.
The one in the foreground is longer than the one in the background, but that is ok - the travel will be limited by the shorter of the two (it's about 10mm shorter, so not a big deal).
So now I guess I have to print some mounts for the motors and the rods... and formulate a plan for the Y and Z axis.