Hello!
I'm not big on searching..if someone asks, I'll provide help. If I know of an article in the forum, I'll just post it.
In regards to the heater core replacement, I've done it in a 2nd gen TA, and in my former 68 Firebird. I did the 68 Firebird in the middle of winter, in someone's cramped garage, which was NOT FUN! It can be done, and I did not remove my fender. However, I did not have A/C. If you have A/C, then you're probably going to have a lot more headaches.
Now, it's been, humm...about 14 years since I did this, but I do remember several things. There are studs on the heater core box up under the dash. I did find removing the glove box door helped more. I dont recall the exact number of studs, but it was like 10-ish. There was one particularly difficult nut that I may have undone the inner fender well for, but I cant remember if it was for that or not. I do know that I was up under the car for 1 or 2 of them. Bright light is your friend
The big things to remember are that the box will need coaxing to back it off the inner firewall. I used a 2x4 block and a small hammer on a couple studs to coax it loose. BE CAREFUL! Dont damage the studs or threads.
If you're going to do this, get the heater box gaskets in advance. While you got it out, you might as well replace them. I used 3M weatherstripping adhesive to hold them in place. If I recall right, there was the outer gasket, plus the flapper door gasket. I also took the time to clean up the heater core box and repaint it.
Finally, there is a retaining device inside the box that helps hold the heater core in place. Mine was pretty shot. You may need to get a new one. Since you're already getting the gasket kit, get that retaining piece as well.
When you're putting the heater hoses back on, it would be a good time to replace them
Also, be careful when putting on the hoses onto the core inlet/outlet, as you could damage them then have to start all over again!
Figure a couple hours to remove the core. I spent day cleaning up and painting the box. Then a couple hours putting it back together. And it was 0 degrees out
