I was very concerned about making sure I drilled the holes perfectly so the firewall was centered. There was lots of clamping and adjusting, lots of testing with the drill prior to actually drilling out the holes. There was a lot of epoxy paint and welding crud that had to be clean/reamed/drilled out prior to the drilling of the firewall. I used a dab of white paint on the tip of the drill to finally confirm that the firewall was perfectly centered. It was a nervous moment, but it went smoothly.