Drilled the top two holes through the firewall for the engine mount. Used a 3/8 in drill for the AN6-24 bolts. I could not find the bolts in my inventory but did find 2 AN6 bolts that I used to temporarily attach the engine mount at the top two bolt locations.
I then realized that the bottom of the mount would not touch the firewall because of the flanges on the cooling ramp area. I used a dremel with a cutoff wheel first to trim off some of the flanges. Then I used a sanding drum on the dremel to continue shaping the edges of the flanges to eliminate the interference. I put the mount on and off several times, triming a bit of the flanges off as I went until it fit.
I marked the places where the holes should be drilled for the remaining four attach points by putting the drill bit through the engine mount bolt holes and drilling just enough to mark the firewall at those places.
When the mount was temporarily in place I determined that I will need to drill a hole in the firewall to access the taper pin that will attach the nosegear leg to the mount. If I ever needed to remove the nosegear leg it would not be possible to do so without taking the engine mount off the airplane, or at least moving it forward about an inch because there would not be enough clearance between the engine mount and the firewall to remove the pin.
