We actually did a lot of work to the firewall. We converted the car from A/C to heat only. We smoothed the distributor recess and filled any unneeded holes. There are still modifications to make as the build continues but at least the foundation is now in place.

Reinforcing the heater box hole mounting flange with 16 ga. sheet metal and re-forming the distributor recess added a great deal of strength to the flimsy sheet metal firewall. You can now hit it with your fist and it rings like a base drum with no rattles. This means all the metal is in a state of tension. Mission accomplished.