Harry, no it does not say safety kettle. I was going by what the foundry link said. Your theory on odorless kettle makes more sense. I've been trying to figure out how the removable front fit into the whole saftey kettle thing. I think your right about it being a vent. Sure would like to see the cover for it.
About the two firms I have no idea, its marked The Hunter Sifter Mfg Co, Cincinnati- O & New York City, Patd 74 & 75. Thats on the removable front, the bottom is gated with a #7. Thanks for the input Harry.