The stock one is perfectly fine until you go to hang stuff off it, like a weapon light. It has what I believe to be a non-standard for AR threaded delta ring. Concerned that an aftermarket handguard might not fit, I got a "Rogers 'Tri-Rail" attachment that fits around the handguard at the front behind the front sight, but its placement is right where my support hand wants to naturally rest and not comfortable to hold.

The Tri-Rail assembled:




Top & bottom handguards, removed:



Delta ring and upper receiver:



It goes together easily, but needs a strap wrench wrapped around it to remove it. There is a great deal of friction between the parts.

This is more to satisfy my curiosity than a true priority. I have a 5.7x28-caliber LC Carbine for actual inside the home defense. Much lighter and shorter, and nobody is going to want to stand in front of a 40-grain ballistic-tip bullet going just shy of 2200 f/s. (I chronographed it myself.) It has all manner of M-LOK holes in the handguard that I can mount a light to.

I used to have a small steel plate that clamped onto the side of the front sight A frame. It had a short pic rail section and a QD sling socket. I'd offer to karma it to you except I haven't seen it since I moved a while back. I *think* I got it from GG&G.

[Edit: Yeah, this is it: www.gggaz.com/quick-detach-slic-thing-qd-sling-and-light-combo-mount.html]

Alternatively, your 3rd photo looks like standard A2 style handguards that clamp into the D ring. If so, something like the Magpul M-LOK handguard should be an easy direct replacement.

You could swap to any handguard you want by tapping out the taper pins that hold gas block in place. Aftermarket handguards come with their own barrel nut. So you would remove the OEM barrel nut and swap to the one that comes with your aftermarket one.

If you want to retain the front sight as it is, you would need to use the same length handguard as you have now. Probably carbine length.

Be aware that those taper pins take a stout whack with a heavy mallet to get moving. And they are directional, the only come out one way.

the handguard looks pretty standard so any system that replaces it should work like Magpul or MW. back in the day I used the surefire m73 picatinny handguard that replaces the stock forened to get actual rails. You may be able to find one of those (I may have one if you get desperate). I've seen people through bolt short picatinny sections to the handguard with a backing plate and that seems to be ok.
Lastly as IndianaBoy says just buy a decent modern forend and junk the whole thing.