Firewall, Vent Inner cowl and side outer cowl removal

[hotrod1]

I am curious if anyone has removed these panels and left them off.

Item #2 and #18 of this URL

http://www.lmctruck.com/icatalog/ca/full.aspx?Page=23

I am building a hot rod 1956 (more like my son is doing it and I am directing) and dont care about the fresh air. We shaved the lip from the firewall and it did not turn out as we wanted it to. When you do this you have the inner cowl and outer cowl and firewall all coming together to form that lip. When you shave this off you have to worry about three pieces and it did not line up too well, and we are not happy with the results. We are contemplating replacing the firewall all the way up to the curve where the rubber for the hood is installed, so it will be smooth and flat all the way down. Has anyone done this? Also, the left and right outer cowl are rusted out at the bottom. Was just thinking about removing them and the interior portion of them as well. This would make a good place for speaker placement after getting rid of those vent doors and misc stuff there.

Do you think that these pieces offer structural rigidity?

Help.