I mounted mine as per the instructions. Mounted the cowl, measured the distance from the center of the face of the cowl to the center of firewall. Added 7/64" and mounted the engine to the mount with those measurements. Then removed the cowl, set the engine and mount on the firewall and remounted the cowl. Then I centered the prop shaft in the center of the opening. Carefully removed the cowl and marked the location of the engine mount and started some pilot holes. Mounted up real nice. I wouldn't worry about the hole in the firewall, just follow the instructions. The hole in the firewall may not line up with the hole in the cowl.