In a recent debate on the authenticity of Mark 16:9-20, James White was asked by a fellow Reformed Baptist if the theology of the passage was "Orthodox" (i.e., consistent with Reformed theology). White stated that, while one can engage in all types of mental gymnastics with the text to make it consistent with Reformed theology, exegetically speaking, it is not consistent with Calvinism, including its teaching that baptism is required for salvation (on the problems of Calvinism, see An Examination and Critique of the Theological Presuppositions Underlying Reformed Theology):
Dr. Jeff Riddle vs. "Dr." James White | Textus Receptus vs. Critical Text DEBATE | Mark 16:9:20 (beginning at the 1:25:56 mark)
This is significant as White believes that vv. 9-20, while an interpolation to Mark's Gospel, is very early (2nd century). This means that, not only does White admit that it does teach baptismal regeneration (a view he believes to be heretical [on this, see Brief Rebuttal of James White on Baptismal Regeneration]), but it is serves as further evidence of how the soteriology of 2nd century Christianity is at odds with his Calvinism, notwithstanding his (eisegetical) appeals to support Reformed theology from early Christian writings, such as the topic of Sola Scriptura and Sola Fide.
Personally, I think a good case can be made that vv. 9-20 are authentic. On this, see
Nicholas P. Lunn, The Original Ending of Mark: A New Case for the Authenticity of Mark 16:9-20
James Edward Snapp, Jr., The Authenticity of Mark 16:9-20
For a Latter-day saint discussion of this passage, see
Jeff Lindsay, Alleged Problems in the Book of Mormon #5: The Problem of the Longer Ending of Mark Quoted in the Book of Mormon
On Mark 16:16 and its affirmation of baptismal regeneration, see:
Baptism, Salvation, and the New Testament, Part 5: Mark 16:16
The Grammar of Mark 16:16 and Baptismal Regeneration
For more articles defending baptismal regeneration from the Bible, see:
Refuting Douglas Wilson on Water Baptism and Salvation
J. Paul Sampley on Baptismal Regeneration and Ephesians 5:25-27
Water Baptism being a Spiritual Circumcision and Baptism being Salvific in Colossians 2:11-14
John Greer vs. the biblical doctrine of baptismal regeneration (Greer, at the time of writing this article, was the moderator of the Free Presbyterian Church of Ulster--texts such as Romans 6 are discussed herein)
The Good Thief on the Cross (cf. Matthew W. Bates on the Thief on the Cross)