The firewall comes with two pilot holes that match two of the upper engine mount holes. The engine mount bushings in the fuselage were drilled out to 3/8". Then the firewall pilot holes were drilled to 3/8". Two bolts were used to hold the firewall in place while I match drilled the firewall and the mounting tabs. There are 5 engine mount attachment points on the fuselage. All 5 are used for a Lycoming 540 but only 4 are used for a Lycoming 360. For the time being I only drilled the firewall for the 4 bolt mounting position. While I am planning to go with a 540 I didn't want to drill the last mounting position until I'm ready to mount the engine. In case I change my mind.
