After match drilling the longerons and bulkheads, I match drilled the firewall brackets with the forward skins. Once all holes were drilled, I removed the skins to gain access to the sub structure. I placed the to front side channels back in place and clecoed them using the holes I just matched drilled. Then I drilled the upper and lower part of the brackets. Now comes the task of disassembly, deburring, scotch bright and prepping for primer.