This was an exercise to determine that my modified PA-18 replica would operate safely at the outside limits at which Piper certified the PA-18. Colin, I would say that this is good in that if, at a worst case situation I was to accidentally get into a spin, that the airplane would be easily recoverable with minimal loss of altitude. In this case the altitude loss was 300-400 feet with instant recovery after one complete turn. This proved that the elevator does not have enough power to force the wing to completely stall at a loaded CG which is forward of the aft limit. This is also telling me that the installation of VGs on this wing will have very little, if any, effect. Perhaps a gap seal on the stabilizer/elevator hinge line will increase the elevator power enough which would allow a spin at a more forward CG.
Tom, The fact that the nose stayed pointed down during the spin indicated that there would be no trouble. If the nose had started to rise towards level (flat) it would indicate that the CG was too far aft. There was no flattening tendency. If the nose had started up there would have been adequate time to terminate the spin safely. A spin is a stall maneuver, which if properly done, produces very little extra loads. The wings are unlikely to depart even in your old 12. The G load did not exceed 1-1/2.