Well a bit of a disappointment when I came into the shop today, but another lesson learned: clay shrinks when it dries.
I had left the clay around the form thinking that it would dry out and I could remove the stryofoam later.
After I removed the styrofoam, I put the pieces back together to see how the lower firing chamber would look like. I'm pretty happy with the results.
Fortunately, the upper firing chamber hadn't dried quite enough to start cracking so I removed the styrofoam mold (the black stain is from where I had to burn out some of the styrofoam with a torch).
I was very happy how this form turned out. In another week or so it should be ready to be fired in a kiln.
The small hole at the back of the chamber is where the pyrometric probe will be inserted. The bump in the middle serves two purposes: it reflects the incoming flame from the burner down to the aluminum to be melted and it protects the pyrometric probe from direct exposure to the flame.