I installed an Adv'd Auto HC (PN 399329), it looked identical. Ended up using 3/8" weather seal from Lowes. A guy in a GM forum said he tested it in an oven at 350 and it was fine (see link).
Finished this project couple days ago. Not the hardest thing I've done, but definitely the most inconvenient. I think the plastic donuts were by far the worst for me. I also spent a lot of time trying to get the heater hose clamps off the HC near the firewall - they were just in and awkward spot with the pliers. Replaced the heater hoses as well, cuz why not, and I used standard hose clamps to reattach to the HC and tensioner fittings. Two flushes with distilled H2O (in order to remove bars leaks I had to use to get home 200 miles), refill, burp, and reassemble.
I didn't reuse the little screws I took out. I just used the 3/4" #6 sheet metal screws for the whole reattachment. I think spazzz referenced these earlier in the thread. They went in fine, no pre-drilling. I did use a drill with a right angle attachment to take some labor out of it.
I'm glad this thread existed, because it truly did help me out, there's not videos on GP's - so thank you to everyone.
http://www.gmforum.com/general-gm-ch...al-kit-308307/
This also visually helped me a little bit before I got started - https://www.youtube.com/watch?v=_cOYV_dy47A
