Reference your comment -- 'The goal is to push the engine back as far as possible to try and get 50/50 weight distribution", I was able to push a Big Block back just under 12 inches, which required building a fake, removable cowl vent to get the distributor out. That puts the distributor (back of the block) just in front of the windshield frame. By moving only the center section of the firewall, I was able to keep all of the original foot and leg room. Rotating the Tremec shifter 180 degrees (to a more forward position) gives a reasonable shifter location. I ended up with just over 51% rear weight, and a little more with the driver seated. There are a couple of pictures of the firewall construction and the driver's side foot well at the link below. Good luck with a great looking project.
Pappy
https://lateral-g.net/forums/showthread.php4?t=21031