Looks like a 3.0l Vulcan engine

Nothing mounts there since this is the back of the engine
Heads can be mounted on either side of a V engine, so casting and machining has to be universal, if this head was on the drivers side then those thread holes would be at the FRONT of the engine, and would be used to mount accessory brackets, i.e. AC compressor pump bracket, or ???

On the back of the drivers side head one of those two holes should have a Ground Strap bolted to it that runs to the Firewall, this is the Ground for ALL cab electrics, so needs to be there and connected


You can use a rubber expansion plug of correct size to replace any Core Plug, factory uses the metal ones because they are cheaper, but if engine is out and you have access then cheaper core plugs are fine to use
But if access is limited then the rubber plugs can be used as they are much easier to install in tight places

 

 

Bummer, can't get enough pounding force to budge it?

It can end up inside the head, doesn't hurt any thing at all, it will just lay at the bottom won't block anything, popular myth, lol.

But sure, you can put on a plate with gasket to hold in the 16psi coolant pressure, should be fine

If you can get a washer and bolt inside that hole you may be able to use those two bolt holes as an extractor base, and tighten the bolt to pull out the plug, as long as it holds

Or a dremel type cutter to get it out

 

 

I doubt there is one that lists all the core plugs, you can buy a Set of core plugs for the 3.0l Vulcan engine

There is a larger one on Drivers side of block and then 2 large on the passenger side

2 or 3 on the back of the block, 2 or 3 on the front

Each head has at least 2 maybe 4

These holes are there to get the sand out after the block and heads have been cast using molten metal in a sand mold
So the more complicated the casting mold the more core holes it has to have

The name "freeze plug" came about before anti-freeze was developed, you had to drain out ALL the water in the engine and radiator if temps were going to get below freezing, all engine blocks had drain plugs in those days.
If you forgot then the water in the block would freeze and the expanding ice inside would push the core plugs out, so they got the name Freeze Plugs
And no they didn't prevent the block from being cracked by the freezing water inside, lol, if the water froze and expanded enough the block would be damaged

Core plugs usually last the life of the engine, and you are correct if one failed, rusted thru, then others may be getting rusted as well
This is because coolant wasn't changed and that causes dissimilar metals to corrode faster, freeze plugs are a steel that can corrode faster, which is actually a good thing since it stems the corrosion in the cast iron and aluminum a bit
Easier and cheaper to replace core plug than block, head or intake.

But unless engine is out of the truck, I would just keep an eye out for leaks around core plugs, and make sure coolant gets changed every 2 years if your using Silicate base, "green color" type