very well done ,I enjoyed it .As a person who built many furnaces over 30 years I never mixed the refractories myself.I always bout it ready mix, it last much longer and less cracking.
I don't have the drawings any more. The whole thing was designed around the outer case of the furnace which will probably be different from what is available to you. Making the drawings was very easy, I'm sure you could make your own.
This particular refractory is not suitable to cast iron temperature ranges. If you contact your local refractory supplier they could make a recommendation and quote you a price on the most suitable product.
Nice furnace, David! We've added it to our Homemade Kilns/Foundries/Forges playlist. If you'd like to show it off to other homemade tool fans (or if you just love homemade tools), you're always welcome on our forums: www.homemadetools.net/forum/?