I did a recessed firewall in our truck but the original firewall was mangled. I was playing around and if I remember right the original firewall is about 4 inches recessed and that is all the aftermarket ones are. Check out Cajundraggers build page, I think he want the 5.3 route.
http://67-72chevytrucks.com/vboard/s...d.php?t=302780
I have some pictures on my build thread also but we are using a big block so some things might be different. It might give you some ideas though.
Let me know if you have any questions. I don't get on here as much as I would like to but I will try to look a little more so if you post something it might be a couple of days before I can get back to you
Bernie