Gas line in an old masonry FP

I've attached a photo of the FP in the exterior wall of my house, built in 1951. You can see the stub of a gas line coming up through the floor which appears to have been placed when the FP was built, presumably as a gas starter for wood fires. Now it's soft and rusty, and could never be used. The pipe no longer connects to the main gas line in the basement.

My question is about replacing it. It seems to me that the pipe must run through a bed of mortar below the firebrick, and so to replace it, the bed of the firebox would have to be torn up. But I'm no expert on 1950's masonry fireplaces.

And if it can't be replaced, does that also mean that a new gas line cannot be placed to rise up into the firebox? I've heard that many older masonry FPs need gas lines run through exterior walls for this reason. I'm just trying to gauge the work needed to install a gas insert.

Thanks.

If you want to put a gas insert in, I'd find the insert first and what side gas is brought into the unit (left or right). Then have a gas guy run new pipe into that side of your masonry fireplace. Make sure he/she installs a shut off valve that is accessible after the unit is installed as it's likely code in your area. Sound be a piece of cake job since the stack is on the outside of your house. They'll just bring a long drill bit made for cutting stone/brick.