Here are some photos showing a few minor adjustments I'm making before I weld in the firewall.
The first one shows the left cowl side where it meets the firewall, inside the car. As you can see, it's a great fit.
My primary concern in these repairs is the proper fit of the doors (of course!). On both sides I fit the doors a few times during the installation process.
I welded in the left panels prior to removing the old firewall and prepped everything for the new one to slide into place. Before I weld in the new firewall I will install the right side panels.
Here is the fit of the right cowl side in place with the door located:
I will alter the bottom of the new piece to take up the gap shown.
Here is inside the car looking up into the corner. You can see where the firewall hits the cowl side before I can mate it to the windshield area:
Here is looking down at the lower corner of the windshield frame. I will trim the new piece where it touches to make everything fit tighter: