Jimdoc,
I like the furnace on your last link. The burner set up is very simple and is very similar to what I used, when I used propane. You just put a piece of burning paper in the chamber and turn on the gas. After a few minutes, you slowly open the air. After a few more minutes, you close the lid and adjust the air and gas until you get about a 2" plume (tail) of flame coming out the exhaust hole in the lid. I used an old upright vacuum cleaner for an air supply.
I hate the way the lid works. I could see myself getting burned. How would you lift the lid without having your arm over the 2200 deg F. chamber? I much prefer a lid that pivots to the side. This can be simply made by welding two short lengths of pipe, one to the lid and the other to the top of the body. A smaller diameter pipe is inserted into these and acts as a pivot pin. Very simple and works as well or better than those common, complicated, lever arm lid raisers that you see on a lot of furnaces.
I would probably use a large diameter piece of pipe (scrap yard) for the body and the lid. I would weld a plate to the bottom. I would use refractory cement instead of bricks. I would weld 4 crossed pieces of rebar inside of the lid ring to hold the cement. To determine the inside diameter of the pipe that is needed, add about 10" to the widest diameter of the largest crucible you will be using. This will give a 3" refractory thickness and a 2" spacing all around between crucible and refractory. The pipe ring is also 3" thick. Some sort of mold must be used to cast the refractory in the chamber. The best is round thick walled tubing made of cardboard. I think they use it for molding round sections of concrete bridges. That way, you can cut the cardboard to remove it. Don't use a metal mold or, you never get it out. When casting the lid, use a tin can to mold the exhaust hole in the center. I prefer at least a 3" lid hole.
Somewhere, in one of my early posts, I went into this in more detail. It is, by far, the simplest furnace to make, maintain, and use that I have seen.