What on earth is an inverted roll? Any rolling manoeuvre that I was taught, be it a slow roll, a hestitation roll or the very simple barrel roll ALWAYS resulted in the aircraft and myself being inverted! There is no other kind of roll.
I would have thought that a Cessna 172 with the big engine would be perfectly capable of doing a barrel roll provided that the driver knew what he was about. After all, the perfect barrel roll is only a 1G manoeuvre.