the gentleman is a little long winded but the design is solid and if you just scale up to a 6" steel pipe it works fantastic
https://www.youtube.com/watch?v=o7bGtQQXNjo
http://canvasman34com.bigcartel.com/products
http://www.ebay.com/usr/canvasman34
the second link is his website. he also has a ebay page where he sells a 4" and a six " version of his furnace already built in full kits, reasonably priced. the jt539 bernzomatic torch heads are a little difficult to find but well worth the money when you do. i traded this gentleman silver for a pair of the torch heads but ive done a good bit of business with him. he will also custom make small custom graphite molds on his cnc mill for a decent value.
the extension propane hoses you can get at home depot for about 15 apiece
http://www.homedepot.com/p/Bernzomatic-WH0159-Universal-Torch-Extension-Hose-334246/202539579
and the propane tank tee you can buy at walmart, dicks, home depot, etc...
http://www.walmart.com/ip/Coleman-Propane-Tee/34761218
and for the upper ring i used tek screws through the ring and the ground the head off the outside so i had 3/4" posts in the refractory