If it was actually detuned, it likely involved putting the small bore 20h carb and intake manifold on it. If the hole in the intake manifold is about the size of a nickel, it has been detuned. If the hole in the manifold is the size of an old Eisenhauer silver dollar, then it's original. The carb venturi (narrow part of the throat) on a 20hp carb is also about the size of a nickel, while the 28/30 carb will be about the size of a quarter.
