1958 Mercury 383 V8
 

I'm new to the group. I'm restoring a 1958 Mercury Monterey with a 383 V8.
I've a question about what appears to be auxiliary thermostats/flow controls mounted within the front of the engine block where the water pump is attached. One has almost fallen apart and the other was stuck. I've removed them both, but wondering what their purpose is, considering the large coolant hole next to these things.

If I do need to replace them, where in the world can I find these components?