I am new to the slant six world. Can someone please tell me what these are?
There is what appears to be a nut on nothing inside the intake just under the carb. What is it and what does it do?
There is a plug with a crush washer in the side of the exhaust manifold under the carb. What is it and what does it do?

Well, Odin.....the first pic appears to have that nut located right where the EGR port would be in the bottom of the intake plenum. Can't say about the nut appearance, but I would try removing it, in case it's just rusted in place.

Your pics are a little too close up for us to really see very much. Back away from the subject a bit and repost.
I suspect that the plug and crush washer may have been a modification to eliminate the EGR valve, but can't commit to that without seeing more of the area in question.
(Another look at pic 2.) No, that's not it, either. Maybe a removable bushing for the plenum heat valve shaft?

Roger

Looks like a newer exhaust manifold that had a bung
for an 02 sensor, which your car wouldn't have had so it's just a plug.

What you've got there is an intake manifold used only on 1972 cars sold in California. The "nut" is officially called the "floor jet", and it is just an orifice (hole) between the exhaust and intake tracts. There is no valve or other control means; the hole is open full-time (until it clogs with soot, I guess). It did the intended job—exhaust metered into the intake tract reduced peak combustion chamber temperature, and thereby reduced NOx emissions to meet California's standard—but those cars ran poorly, as you might imagine. The following year, 1973, the NOx limit went federal and the Slant-6 in all 50 states got a much more sophisticated exhaust gas recirculation system with a shutoff valve controlled by a system intended to allow exhaust recirculation only under conditions when it was actually needed to curb NOx formation in the cylinders.

You can replace the floor jet with an appropriate solid plug, or use a manifold without this provision.

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Thanks for the replies. They are helpful. The port on the side of the exhaust matches what would be an O2 port so I’ll go with that answer. The nut/port in the bottom of the intake under the carb isn’t an opening so I’ll assume it is full of soot based on the provided response. I’ll leave both openings mentioned plugged as it seems to the best way forward.