You stated a hypothesis that the Fathers and Doctors of past centuries would wholly agree with the teachings of Catholicism as it stands in 2006, even though their writings during their life indicate disagreement on specific issues. Hans Kung and Nicholas Gruner are men in 2006 who do not wholly agree with these teachings. There is no need to speculate as to where they stand. I further understand that Father Gruner may presently be in active disobedience to his ecclesiastical superiors. How then, given the definition in Lumen Gentium, can these men be Catholics?
As for Gruener, he is suspended a divinis due to his disobedience. I don't know much about any heresies he might be attached to
Frankly, we are far too lax :)