Hi there. I have one of those clone super-6 carbs, but I'm using it on a 318. The carb has, by my count, 8 ports of various sizes, although I'm only using 3 of them (PCV, distributor, choke).

There is one port that comes off the back side of the throttle plate, a small port about the same size as the distributor or choke port. I use it to make manifold vacuum measurements but otherwise it's capped. But I've noticed that when running at warm/hot idle if uncapped the RPM's go up a little. I've also noticed during cold starts that if uncapped the engine runs a LOT better / faster. Some say this port goes to the warm air control valve on the air cleaner housing, so it's not really meant to flow air. But I'm thinking of leaving it open, maybe plumb it to -

plumb it to the single small port I have on the underside of my air cleaner. This port is a mystery. My air cleaner has no valve mechanism of any sort, but it does have a SINGLE port (nipple) on the underside, I seem to recall that it was connected to *some* port on the car's orignal BBD (circa 1967, this was a poly 318 originally).

So this is basically 2 questions. Is it possible that this Super-Six clone is supposed to have a small throttle-body port that is supposed to flow air, and where would the small port on the air cleaner connect to on a 1967 BBD?

I've not seen a copycat Super-6 carb, only copycat V8 carbs. Want to show us what you got? Link/pics.
Thermostatic air cleaner vacuum feed, assuming "back side of throttle plate" means under rather than over the plate when it's closed. Because you've created a vacuum leak. Because your choke pull-off link is in need of adjustment (close the legs of the U-bend to make it pull the choke open more). No. We don't leave ports open to the (dirty) air.
No. But show us pics of this air cleaner port, please.
No.

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Too many people who were born on third base actually believe they've hit a triple.

Here is a pic of the carb:
Here are some views showing the ports:
Port 4 is the one where if it's open, the warm idle goes up a little, and when cold starting the engine runs much faster right off the bat. I'll connect a vacuum guage to this port to measure manifold vacuum. I'm currently getting 18 or maybe 20 inches at warm/hot idle, timing is 10 BTDC. I must say that turning mixture screws don't seem to have much effect at idle, I'm not finding a setting that gives a sharply-defined smooth running and peak vacuum like I remember from years ago when adjusting other BBD and the BBS on my slant-6.

Here is the bottom of the air cleaner:
Close-up:

That's a copycat version of a '77-up "solid fuel" BBD. Can't see the telltale choke lever configuration because there's no pic from a suitable angle, but looks like probably a copycat 318 carb; where does the idea come from that this is a Super Six carb clone?

Port 8: venturi vacuum tap for EGR, not used in your application; cap it.
Port 7: fuel inlet
Port 6: bowl vent
Port 5: distributor vacuum advance (probably; can't 100% tell from this angle)
Port 4: manifold vacuum to thermostatic air cleaner, not used in your application; cap it.
Port 3: canister purge inlet, not used in your application; cap it.
Port 2: choke pull-off
Port 1: PCV inlet

Nipple on underside of air cleaner means you have an unusual air cleaner, configured for use with a heat-tube type automatic choke or a throttle anti-ice system. Not used in your application; cap it.
Bit much, back off to 5°.
This might change once your initial timing and idle speed settings are corrected and unused ports are properly capped.

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Too many people who were born on third base actually believe they've hit a triple.

Port 7 is another vacuum line under the fuel inlet. A bit hard to see in one pic.

I'm not changing my timing. If I get great stable low-speed idle and great vacuum at 10 BTC on 87 octane ethanlol junk then it's staying at 10.

These engines waste so much gas when idling, the slower the idle the better.

Current state of mixture screw "unresponsiveness" is with all ports capped as recommended, PCV is connected, bowl vent is open, and with timing set at various between 0 to 10 BTDC.

I'm considering buying an air-fuel ratio guage, which involves mounting an oxygen sensor in the exhaust pipe. There is one on amazon described as "30-0300 Wideband UGEO Air Fuel Ratio Gauge 52mm(2-1/16"), AFR/Lambda Controller Kit with LSU 4.9 Sensor" for $170 CAD, seems highly recommended.