I'd try mixing Wollastonite and Phosphoric Acid and pressing it into a mold with the groove indentation already in the mold. It becomes hard after 20 minutes or so and cures fully at 550F. http://cone6pots.nin...phosphoric-acid
It's generally porous enough to stick kiln pins into and stable up to 3,040 F. But you can mix in pumice stone or soft fire brick ground up to end up with something a little less strong and easier to stick pins into. These are slightly different starting ingredients to kiln repair cement you'd buy from your kiln manufacturer.
Someone mentioned a calcium-phosphate or magnesium-phosphate cement at Home Depot that may be less expensive. I think most are two part cements mixing Ammonium Phosphate with Magnesium Oxide or Calcium something. But that's what you're looking for, a phosphate cement.
Norm, I am getting closer to converting the pieces/parts from two old electric kilns into a propane, updraft gas kiln... very similar to this project: http://codyopottery....irth-of-my.html After looking at the hole in this guy's kiln where the propane is introduced, I'm considering molding a pipe that would slide through the rectangular cut in the side of the kiln, basically rectangular profile pipe on the outside but round in the center where the gas flame would pass through. Would this Wollanstonite-Phosphoric Acid mixture work for this? If so, what sort of mold release would you recommend?
Burner ports are a great place for castable.