Your AC and CG calcs are correct, but DO NOT trust that neutral point. It is based only on areas and distances. There are several factors that will move it forward.

1. The stab is operating at a lower AoA than the wing due to the latter's downwash
2. The stab has a lower aspect ratio, further reducing the lift slope of that surface
3. Propeller thrust will cause de-stabilizing pitching moment if the prop is ahead of the CG.
4. Propwash will further reduce the stabilizers AoA making it less effective.

Any calculation of the neutral point should be made for a flight condition offering the least stability (high AoA and high power)

For example, at 15 deg AoA

Wing CL = 1.2 (corrected for AR = 6)
Downwash = 3.6 deg
Stab AoA = 11.4 deg
Stab CL = 0.8

Already, the stab is operating at 67% efficiency, moving your calculated NP 3.5" forward. I would need to know the distance from the propeller to the wing's AC, the prop diameter and some power estimate to factor in that stuff.

It's always a good idea to start at 25% MAC and go back from there based on flight tests.