The distance from the firewall is measured at the the centerline of the crank shaft. Normally it is called out as the distance from the firewall, to the front of the thrust washer, not the prop. Left or right thrust does not enter into the equation; but, does make getting the measurement more difficult. The plans show the engine installation from the port-side and from the bottom of the airplane. The plans show you where the engine mount is located on the firewall. Mount it there and it should stick out of the hole in the front former.

Making all this more convenient is the fact that we don't have to worry about the front of the fuselage meeting the back of a spinner! Basically if you have the thrust washer and prop clearing the front of the fuse, you are home free!

If you can grasp all this, then you may be able to help with the airplanes balance, by sliding the engine in or out.

The honest truth is I don't understand what you are asking! I tried to give you enough information on engine installation to help you through the process.