While I'd like to know where GPH gets these excerpts from too, (I doubt he has stacks of hard copy books containing all the ECF's writings but that's just me) this question seems largely irrelevant, IMO.
What I find interesting is that you, GPH are commenting on the following section from the OP:
A view most supported by Mormons and Jehovah's Witnesses is that, after the Apostles, the Church quickly fell into apostasy. This would be a massive blow at both God's promise to guard His Church (Joshua 1:5; Matthew 16:18) and all of the doctrine mentioned hereafter. But if this were true, would not one of the disciples of the Apostles have spoken out? We have writings from many of them, including Pope St. Clement I, St. Barnabas, St. Polycarp, and St. Ignatius of Antioch. None of them mention a "Great Apostasy".
You quoted the portion in bold and then proceeded to post excerpts from the writings of those mentioned to "prove" they all held some kind of paleo-Protestant viewpoint (I guess) about the topics of predestination, final perseverance, sola fide, and the immutability of God's will.
The point is why? Why would you do that and not address the overarching point of the OP of this article and tell us all, though the Fathers (can I call a man "Father"?) when the Catholic Church fell into apostasy? That is the point of the OP after all and you yourself ask, "The real question is, when did the Romish church apostatize from the faith?"
So don't leave us in the dark; tell us when it happened. Or do you agree with the JW's and the Mormons, that there pretty much never was any church to begin with, and only until people like Matt Slick and his website CARM came along, we now have resurrected the "faith of our Lord Jesus Christ"?
Or are we predestined to Hell anyway, and thus not worth spending the time actually discussing the point of the thread?