Here's the firewall with no cuts yet. Notice that the angles and sheet are NOT stock. This is part of the reason I wasn't too worried about cutting my car to fit the engine.
Always measure first. We had some reference photos from Pantera Performance Center that illustrated where to make the first cuts.
Here I am, cutting away. I tried to keep out of the plane of an exploding cutoff wheel.
Now I'm cutting the driver's side.
Here's the finished cut opening.
Here's the first round of cuts at the passenger's side valve cover.