The oldest surviving Greek manuscript that has the account of the woman taken in adultery, in John 7:53-8:11, is the Codex Bezae Cantabrigiensis, which dates from the 5th century A.D.. I use the word "surviving", because when the scholar Jerome (A.D.347-420) wrote on this passage, he says that it was present in, "in many manuscripts both Greek and Latin". (
c Pelag. II, 17). It is found in the Old Latin and Vulgate, the former representing a Greek text of the 2nd century. Augustine says of the passage, "Certain persons of little faith, or rather enemies of the true faith, fearing, I suppose, lest their wives should be given impunity in sinning, removed from their manuscripts the Lord's act of forgiveness toward the adulteress, as if he who had said, Sin no more, had granted permission to sin"
On Acts 8:37, and the confession in Jesus Christ by the Eunuch, it is quoted as Scripture by Irenaeus, as early as the 2nd century (130-202), in his Greek New Testament. And Cyprian, Bishop of Carthage (210-258), who, though of the Latin Church, also used the Greek New Testament. It is also in the Old Latin, and known as Scripture to Augustine.
1 John 5:7, which is the best and clearest single text on the Holy Trinity, is beyond any doubt part of the original autograph by the Apostle John. I have done a study into the Greek grammar of the passage, in which this verse is, and shown that there is no question that it has to be genuine.
http://www.trinitystudies.org/Trinity/1jn5.6-10.pdf
On the ending of the Gospel of Mark, no one has in over 100 years, be able to refute the great work on this passage by John Burgon,
https://archive.org/details/lasttwelveverse00burggoog IMO it will never be proven as not part of the original Gospel of Mark.