It's difficult to tell the thrust line from the photos.  If anything, it appears that the engine is shifted slightly to the left side of the fuselage (This is what you want anyway to add right thrust).  If so, then a shim can be added to give the right thrust, but you will have to rework the fuselage to recenter the plywood ring to the spinner.

The best way to determine the thrust is to measure from a large prop tip to the tail from both sides when the prop is horizontal (make sure the prop is true by taking the first set of measurements, then turning the prop over half a turn.).

If they call out right thrust, you want to have it.  Otherwise the airplane will not track true when you pull into vertical.