You got that on the nose, you may need a few torx style bits (sockets). My father and I tackled mine in my 88gt in about 5 hours, that was changing the evap too. Take your time. I dropped the steering column, and disconnected the dash but just moved the dash foward enough to get the hvac box out of the car. When you reassemble it, make sure you are not pinching any wires or vacuum lines, and if you have a/c make sure that the drain tube for the evap goes out the hole in the firewall. Good luck, take your time.
Nick
p.s. if you have any probs, email me or pm me, and I'll see if i can help.
I did mine in my 86. Make sure you have patience and time! I pretty much rebuilt my dash, good time to do some heavy cleaning in there too while you have it all torn apart. I also used insulated duct tape for vents to wrap my vents where they snap together "no leaks".
It is possible to not disconnect any A/C lines when changing it. I just did mine without disconnecting them. When you unbolt the evap from the firewall, just bend the metal tabs back and slide it off. Then bend them back on when you're done. It's more difficult this way but you don't need to drain your A/C. If it's already drained...
And yes it is a PITA. I'd stick a rag in the Venting in case (when) you spill anti-freeze anywhere. I didn't and it smells wonderful now
Like 1986LX2002 said, I siliconed all my A/C vents, no leaks is super
I got lucky on the last one i did. My 86 dosen't have ac and there is a little box right under the glove box the the heater core will slide out of.
You shoulden't have to take the dash all the way out. just take the bolts out and slide it back as far as you can. My brother has this down by now. He got two bad heater cores before he got one thak diden't leak. good luck and takeyour time