Shaved firewall help

[camaro2nv]

So far so good! My first welding project has been going pretty good. Its been a good learning experience. Ive good pretty much all of it done but the tunnel section. I havent welded it yet because I dont know how high I have to go to fit the LS2. To those that have done it how high did you go up? Past the stock arch so lower? Did you make a new tunnel to weld in of worked the stock firewall to fit? The goal is to keep it as smooth as I can. Thanks for any bit of info!