Nope, not the Judas Priest song... A fellow classic mini-afficianado who also has a Giant asked me about making him a jaw: his was long gone (it is the smallest loose casting in the set). Very fortunately I was about to pin and epoxy it to the skull and make the two pieces one, he got me in the nick of time.
A little 'squash' mold was prepared (nothing to fancy, two halves filled with more than enough casting material and pressed together, squeezing out the excess).
I did something I had not done before: I tested the mold with another material (other than the resin to be used for the final) - JB Weld, a two part substance I found at a hardware store that is supposed to be great at fixing metal parts (never had any luck). It's a great filler and worked well for determining if the mold performed well enough to pull a decent cast.
The subsequent (white in the photo) resin jaw came out fine, and I'm free to finish assembly on the skull. The gray jaw is the JB Weld piece.