Hey John, that's an interesting approach. I don't know much about machining stuff, but that pic got me wondering about coefficients of thermal expansion and production.
According to
About.com: http://www.handyharmancanada.com/TheBrazingBook/comparis.htm there are some ceramics that have low expansion, possibly ceramics are fuel resistant too, dunno. But not hard to imagine making a mold and baking the parts. Have you ever messed with ceramics? I'm a total nube to the idea, except for pinch pots and stuff
Maybe that circulating ball and track can be done that way? I have no idea.