I would also be very interested in a furnace for metal casting. The backyard.. site you mention above has lots of good stuff on it.
I've dabbled a little bit with casting with zinc from pennies in a small charcoal fueled furnace I made. It was wicked fun.
It looks like building something on a dolly is a pretty good way to go. This gives you a sturdy framework to mount stuff to, and a nice big pair of wheels to play with.
Most of the designs I've seen involve using either a 5 gallon metal bucket, such as some adhesives or flooring goop come in, or instead a propane tank.
If someone else doesn't make one of these, I'm going to, and hope I can keep it at the space.
Metal casting works really slick if you have a cnc that can work on pink foam. It eliminates the need to make wooden patterns for one off castings. Simply shape your positive out of pink foam, glue on a plank of foam to act as a "sprue", submerge the pattern in a bucket of sand, apply melted metal, and bang! there's your part.
If anyone does start moving forward on this, let me know, so we don't needlessly duplicate effort.