I continued working on the piece-parts for the firewall. I calmped F-601E to the firewall and back drilled the holes.
For F-601P, I used the stiffeners as a drill guide. The parts were clamped in place and match drilled.
I rounded the edges of the brackets using my grinding wheel.
To back drill the F-601J bracket in place, I used a 3/32 drill bit to ensure the correct spacing from the bottom stiffener. The parts were clamped to the vertical stiffener. 
I used drill bits the locate the holes of the spacers. This was pretty effective before I could match drill everything.
Here’s the final math drilled bracket. Looks pretty good to me.
I match drilled other miscellaneous parts on the firewall.
