Wrapped a ratchet strap around the firewall, ratchet at the bottom and snugged it up. Took some 1/8" thick paint stirs and started shoving them in the open areas. Once I got it as close as I could then made the curved (7 crimp) L-angles.
Pilot drilled curved L-angle intersections and clecoed in place. Pilot drilled firewall flange intersections, made the 3 L-angles for both left and right sides.