You can patch that. It is actually the top of the firewall. Like poison said, you can bend and shape metal. Its actually called shrinking and stretching. Its really not that hard. I took a lower patch panel for a Duster 1/4 and formed it to fit my 68 Cuda without to much effort using a leather lead shot bag and a body hammer.
You can do it! If you have any questions just ask here on the forums and many will be obliged to give a helping word. It really is easier than you think! Just take your time. My Cuda has been in the Resto/Mod phase for nearly three years. I have threatened several times to sell it but it hasn't happened yet! LoL!!