I'm putting together a Lanier Citabria ARF and am getting ready to mount the engine to the firewall. The kit instruction manual says, "Align the mount and motor assembly on the centerlines of the firewall and mark the correct locations for the holes." Where are the "centerlines of the firewall"? The firewall has no marks on it at all. Does anybody know what they mean here?

Also, should the prop spinner line up with the centerline of thrust or should the engine mounts line up with the thrust line.

Thanks,
Les