Cami, the link you posted is basically exactly what I have done. The only difference is that mine are plaster and my injection and bait are in-line so I am pushing straight down toward my bait.
Vodkaman, I have been looking for good information about the vacuum method. The first mold that I made I scraped air canals to all of the little pieces and then connected them to a vent hole. But I did not like the look of it so I scraped it. I am hoping this works. Also, I made my plaster molds extra thick to compensate for any pressure. Both halves are close to 2" thick.
I know that it will require extreme attention to safety for sure, I will prolly make an aluminum foil shield around my dowel to minimize any splatter that may shoot out of the injection port if an air bubble tried to come back up or if it squirted under pressure. I am glad to see that in all my tinkering I may not have wasted my time! I bought some Silicone today to try to make a silicone open pour mold just for fun, I am excited about this hobby!