Before you start modifying the engine mount, make sure that the thrust line are "NOT" built into the firewall. If they are, you just center your mount and attach it. Most of the current kits will have the thrust built into the firewall. Even built from plans planes will have the thrust line buitl in. Just check this out closely before making that adjustments with the mount. You could easilly turn a 2 Degree thrust into a four degree one

Don