In my uncle's build, he has added a firewall here, and I think I am going to as well. The first step is to make rough templates for the pieces that will make up the firewall.
Here's what I came up with. It all assembles pretty well onto the car. It's just slightly rough in a few places, but this is a pretty good draft to work from. I need to buy some 0.060" aluminum and start cutting things out.