I used 1/4-20 rod couplings that you can find at HD or Lowes. and then I welded them to the inside firewall so I didnt have any bolt heads on the engine side. Make your plate first to fit all your stuff and then do the mounting holes to the firewall. Just tack them first and remove the plate and then weld em tight!
I put my main fuse box and CDI ignition box on one plate there in the upper drivers corner.
