Converting Vented to Ventless... Is this even possible?

Hello everyone. Hopefully someone can shed a bit of light on this and help me out.

Basically, my house was built around 1991 with a vented fireplace. When I had my roof redone a few years back I had the vent removed and turned the gas off for the fireplace figuring I'd replace it later on. Now I'm looking to replace said fireplace and it's looking to be nearly impossible...

The problem is two-fold... First off the fireplace is actually stone build around the insert. Of course, to fully remove the fireplace the rock would need to be broken away. The second issue is how this is a corner fireplace that's about 21" long. My original hope was to simply remove the fireplace and put some ventless insert in there but I'm guessing this isn't possible...

The unit in question is a Heat n Glo 6000TV.

https://i.imgur.com/KvBH6aJ.png