In the purebreed PA-11, at the fuselage where the wing root meets it there is less inclination downwards than in the J-3. In other words, an original J-3 or a converted one the back of the cockpit and the fuselage is not as straight as in the case of a true PA-11.
The PA-11 is my favourite aircraft; it flies on its own, like when I took this picture with my two hands, and none at the stick.
These are indeed, details, but they all add up to a fact that anyone will notice while flying a PA-11: It is a superb, flawless aircraft, but a purebreed is even better than the converted ones.
Another inflight picture showing the pedals; the stick is dead on centre and the machine flies by the hand of God.