What is this thing?

Just finished putting the 300 back in the 81 project and getting ready to start hooking stuff back up. It's been so many many months since I first put it on the stand that I don't even remember the process of pulling it, including apparently breaking/sheering off this thing in the photo. Can you give me a name for this part? Thanks in advance.

That is the EGR adapter plate.

Thanks for the quick response, but I'm not asking about the spacer but the bowl shaped thing threaded into it hanging just above the manifold, with the jagged open end that might have had a hose connected to it at some point or might have had metal tubing that was broken off.

that is the air injection check valve. it takes air from the air pump for the thermactor system and pumps air in for the exhaust catalytic converter. if you are not intending to reinstall the air pump you can remove it and plug the hole with a 3/4" npt galvanized, black or even brass plug. the part to be careful about is the egr plate that is screwed into is aluminum and often the steel fitting can strip out the threads when being removed

I put an aluminum one in it from summit. I want to say it was $4. Probably never going to reuse it for it’s intended purpose but I’d prefer the plug not get corroded in.

anti-seize

Thanks for the info. So, two follow-up questions:

1. I made an attempt to unscrew it from the body of the spacer and it is quite stuck in there. Any tips for removing it without damaging the threads, as you mentioned?

2. I'm pretty new to this type of rebuild, and I've come across quite a few videos and articles/threads about egr delete. Is that a good idea? What are the benefits? Will I pass emissions? I'm in Texas.

there are two different circuits going through the egr spacer. egr of course and air injection. not really related although there is a bit of cross contamination in the exhaust manifold. nonissue!
as far as removal, a good penetrating oil or heat supplied to the steel fitting may help. i don't like to torch an aluminum casting. but directly on steel I will do. the aluminum will heat sink .

 a properly working egr system is a benefit. is it necessary? no! so many engines do not have them and run just fine. I have deleted many. but understanding why the manufacturers spend so much making them and so on is valuable info. we know that the engine requires fuel, oxygen, compression and ignition. if we have all of these, we will have an engine the runs. running engines generate excessive heat requiring a cooling system, and an oiling system to reduce friction and friction generated heat. we use our engines across a wide range of loads and conditions and for the majority of the time we use fuel we don't need to and generate heat we don't need to. during these mild load conditions, exhaust gases are allowed into the engine through the intake to take up partial volume in the combustion chamber which lowers compression slightly, lowers available oxygen by volume, lowers available fuel by volume and lowers combustion temperature as a result. effectively cooling the engine, reducing fuel use and also emissions. this also reduces the chance of pre ignition "pinging" and the harmful damage from it. all of this has a major effect on WARRANTY issues. making engines more reliable and less expensive for the manufacturer.
all of that said, whether or not I use egr is dependent on what I'm building the engine for. plain and simple. if I'm driving it daily, if I'm working the truck, yes, I keep and maintain egr. if I build a toy where I may play and "experiment" then I will delete all secondary systems except what is part of that specific build .