Not sure of your concept, if the metal rods are like vents to let the gases out from one jig to another it might work but the problem I see would be keeping the plaster hot enough (without cracking)and as not to cool down the lead or what ever metal you are using allowing it to flow.
I did a lot of casting in gold and non precious metals and the weak link in the system always was the mold material. In my case a form of plaster only it was cured at around 1800 degrees or so.