OK, by the book, yes, a dash out job.
But it can be done without that.
I got my old leaking core without removing the dash. I did take out the driver's seat however as I'm not as flexible as I used to be!
When you get in to the foot well, you will see a metal bracket that holds the
HVAC system in place. Unbolt it, and put it to one side.
The pipes that run off the back of the core go through the firewall. In a full dash out change over, you pull the core and pipes through the firewall after disconnecting the rubber tubes inside the engine bay.
But if you're up to it, you can leave the pipes in place, and cut through them, either with a dremmel tool, or with a small hack saw blade. Before you do this, make sure the engine is cool and you have clamped off the rubber tubes in the engine bay, to reduce coolant going all over your carpet.
Aim for about 2/3's between core and firewall. The 1/3 is closest to the core.
Once through, you can litterally slide the core out towards you with a bit of jiggling.
Once you have a new core, or a second hand one, lay the two together, and cut the pipes at the same position. Try not to get any metal shavings in the core.
Get a piece of rubber heater hose, just bigger than the tubes and slide it on to the 2/3's sticking out the fire wall. Put two stainless circle clamps on there too.
Put your new core in place, slide the hoses down, clamp them on.
You might want to get a small piece of rubber mat or something like that to act as a barrier if the clamps ever fail, as you dont want to be sprayed with hot water as you drive!
Put the metal bracket back in place and top up your fluids. Let the car run for a bit as there will be plenty of air bubbles.
So it's not for the faint hearted, but a lot more simple than a dash out job.
I did my LT over 4 years back now, and havent had any issues.
Best of luck with it.