ORIGINAL: Crashem
If your wing is rubber banded on I'd measure from the tip of the horizontal stab to a point at the tip of the fuse that way provided both sides of the fuse are equal in length you don't have to worry about making sure the wing is square and centered with respect to the fuse.
Yup ... and don't use the spinner etc as your refernce, since the engine may have a non-zero thrustline.
The way I do this part of the alignment check, is I stick a pin into the centerline of the fuselage, near the nose of the aircraft. Then I attach a (non-stretch) string/thread/etc to the pin, and then I pull the string out to the reference point on one stab tip and "mark" that point on the line by holding my thumb-nail on it - then swing the string out to the other side and compare it; make a slight adjustment to the stab to "split" the difference, then repeat.
Gordon