I'm picking up the new core tomorrow morning.
Also swapping in a used clutch pedal set-up while I'm at it.

 

I'm more than half done. I made pics, I'll post them when I'm not so hot, tired and dehydrated. This isn't a difficult job, really. Nowhere near as bad as trying it with a second generation F-body.
Working carefully and methodically, it took me 5 hours to get the old core out, basically by removing every bolt and screw I could find. Very few didn't really need removing, but no problem.
The kicker is the one you can't access without removing ALL the HVAC stuff underhood, and some of those fasteners are under the carpet.
The replacement core I got isn't such a great fit, and I suggest you find another brand. This one is a Proliance Ready-Aire.

 

most of the aftermarket cores arent a great fit and require some sort of modding to get it in and working.

 

I didn't find any need to make any modifications.

 

then you got one of the better ones. the one i got the end tanks were a larger than the stock core and rounded, so I couldnt reuse the metal hold down peices.

 

i replace dmy heater core last winter, what a P>I>T>A a haynes repair manual helped me alot, that and patience, also i did not have to pull up the carpet or remove the kick panel, however i must have done something wrong as my dash now "sags" on the passenger side

 

Sags? Like the top falling rearward?

 

more like the actual "dash" (where the glove box leather pouch is) is sitting low and i bang my knees on it, i think one of the supports is loose, or i "bent the plastic" when i put in my new heater core

also theres a noticable gap between the dash and dash pad, as well as the dash and the door

 

I just recently did my heater core. I also purchased the ready-aire brand and it was a POS. Did you get it at Oreillys? Anyways i returned it and went and bought one from my usual auto part store for 10 dollars more that was identical to the original.