last night I completed all the prepping of my firewall, sanding down with a 400 grit and then wiping down with a degreaser etc... and sprayed on several coats of
a satin black that turned out just a little too shiny. I have two questions, first has anybody found a spray can paint that duplicates the factory black and second, would it be necessary to go over all of the firewall again with a 400 grit sandpaper before I repaint with a different color?

You, like a lot of us, has found that a spray can will do the job sometimes (at least temporarily). If that is what you prefer, two things:
Always scuff up a layer of finish paint that is not still tacky between coats.
And, as for the paint, Krylon semi-flat black looks awesome, but like most rattle cans, doesn't last long. Might I suggest POR15. It's in my shop, but not on the car...yet. Got it based on my search of posts here. Feedback guys??

I used ACE hi temp semi gloss grill paint as in cooking grill. Looks great IMO. It's holding up better than the fancy "manifold" paint I got at a swap meet. It's been a year and they are rusting. http://www.chevelles.com/forum/mad.gif

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my 67 droptop (http://www.mdesignstudio.com/chad/other/mychevelle2.jpg)

Dad's 67 droptop (http://www.mdesignstudio.com/chad/other/dads67.jpg)

Use the Rust Tough version of the Semi flat black- its alot tougher than the regular version.

I used the Krylon semi flat and it looks terrific!....I went over the entire surface with 400 then wiped it down with lacquer thinner masked it all off and put a few coats on......let it dry over night , wet sanded it again this time with 600 and a couple more coats.....looks like it just rolled out of the factory paint booth! Thanks for everything guys!