Novice question about intake manifold
 

What is the item to the left of the thermostat housing and what does it do?

Thanks.

It’s a thermal switch that controls the vacuum advance in relation to what gear the transmission is in.

Does it matter if the transmission is auto vs manual?

I forget, I am not home to consult my manual.
Most folks do not even have the needed vacuum solenoids any more that the switch controls, that much I can tell you.
Also this set up was only for emissions purposes.

Yes, it's for the TCS system. It controls the vacuum advance based on water temp and also what gear your in and I thought it was used in both auto and manual cars. I have mine in place just for appearance but it's not functional, I don't have all the other components and personally, I think the motor runs better on manifold vacuum. Like Steve said, it was done purely for emission control.

Here's a better explanation of how it works from @Joe's Garage:

If the system is functional it energizes the solenoid that allows full manifold vacuum to the vacuum advance when the engine is very cold - helping with the choke system and idle during warmup.

It also energizes the solenoid if the engine gets too hot either at idle or low speeds - applying full vacuum advance and increasing the idle speed to help with cooling the engine back down.

In addition to this coolant temp sender activating the solenoid, it is activated by either a speedometer cable switch (on automatic transmissions) or a switch on the 3-4 shift lever (on Muncie transmissions) to allow full vacuum advance only in high gear on automatics or 3-4 gear on manuals.

If I'm not mistaken it also ports vacuum to the flapper(s) on the factory air cleaner.

Vacuum to the "flappers" on the factory air cleaner is taken from the #1 runner on the intake. It has NOTHING to do with the TCS system.

FWIW

And is the most common vacuum hose left off by mistake as sometimes even pivoting the air cleaner base around to drop its locating tab in the carb will pull it off.