What?s this AR part called

[that one guy]

So just to confirm I’ll need a fixed stock and a monster man grip thing. The parts I’ll need to swap will be a standard rear take down pin,bolt catch,spring and detent. Is there anything else I’ll need for the bolt catch?

[that one guy]

Bolt catch
Bolt catch roll pin
Bolt catch spring
Bolt catch plunger/buffer?

[ar15barrels]

Bolt catch
Bolt catch roll pin
Bolt catch spring
Bolt catch plunger/buffer?

I looked at your pictures again and you already have a bolt catch which means you likely have the roll pin, spring and plunger too.
That means there is some OTHER device in your lower that blocks the magazine catch so you can not change magazines without disassembly of the action.
Or perhaps your rifle is simply illegal now if it does not have such device.
In either case, when you go to featureless configuration, you will not need a locking device.

You can fix your current collapsible stock with one of these:

https://www.strikeindustries.com/si-ar-stockstop.html

It is a molded piece of rubber that makes it so you only have ONE position that the stock will lock into.
You cut it to the length that you want your stock to be fixed at and then slip the remaining two pieces into the slot on the bottom of your buffer tube.

Measure your barrel from the end of the A2 flash suppressor down the bore to the boltface when the bolt is closed on an empty chamber.
You can drop a cleaning rod down so it rests against the boltface and then wrap a piece of masking tape around the rod at the end of the A2 flash suppressor.
Then pull the cleaning rod back out and measure the length from the tape mark to the end of the cleaning rod that was touching the boltface.
If you find it to be around 17.3", you probably have a 16" barrel and the A2 flash suppressor will just unscrew.
If you find the measurement to be less than 16.5", then the A2 flash suppressor is likely permanent attached to the barrel so you will need to cut it off and then perm attach a new muzzle device to keep the barrel over 16" length length.

I do this type of work if you need someone to do that for you.

[OlderThanDirt]

It has a A2 bird cage on it.

The bird cage is a flash suppressor that will need to be removed. Look at AR15 barrels? advice on how to deal with this issue. Looking at the most recent incarnation of the LWRC IC-DI, it looks like the barrel is 16.1 inches, so you can switch the A2 bird turd with a muzzle brake or thread protector.

[G-forceJunkie]

LWRC uses their own system machined into the lower, sorta like the Hogue Freedom Fighter system.

https://www.reddit.com/r/LWRC/comments/vx1zpb/has_anyone_removed_the_california_plunger/

Just remove the plunger. No actual need to remove the Hellfighter pin unless you want to have the stock pin.

That means there is some OTHER device in your lower that blocks the magazine catch so you can not change magazines without disassembly of the action.