DJ - I have enjoyed reading through your site from time to time and have had a quick look but can't see an answer to my question; it is about the Mount of Transfiguration before Christs' atonement. Clearly He had to leave the apostles with the authority to lead the church after he was gone and I had always regarded the event at Kirtland as the modern day equivalent of that prior event. A closer reading of the accounts of both records raises a question, namely, where is the third key in the bible account? In Kirtland Temple there are plainly three persons conferring their particular priesthood keys while in Judea there is mention of building three altars; one for Moses one for Elias (Elijah) and one for thee (Christ) inferring there was only two other persons there. My thinking is that there WAS three but over time Elijah and the real Elias have got mixed up and have become one in that record. Another possibility is that as literal descendants of Abraham they did not require the "keys of the dispensation of the gospel of Abraham" or that Christ stood in for the real Elias, but this last one is unlikely because it would be out of order for Christ to be a rep for anyone except Heavenly Father, and I presume He could have conferred all the keys Himself if He was directed to. So what do you think? Are you able to shed any light on these most important events?

JOEL - Christ could have of course done it all himself, but as we have learned throughout the scriptures He likes to delegate responsibilities out to His servants the prophets.
The record of what happened on the mount of transfiguration I think is as you have suggested, fragmentary or incomplete and even somewhat contradictory, especially when one considers the JST version of the event. This makes it difficult to know exactly who was there and what happened. It's also hard to know who is being spoken of when the name "Elias" is used. Elias can be both a name and a title that can refer to any one of several people.
We know that Moses and Elijah the Tishbite(1 Kings 17:1) were there on the mount as translated beings, which made it possible for them to give the keys of the kingdom to Peter, James, and John. Elias is simply the New Testament Greek form of the Hebrew name Elijah.

"And, behold, there appeared unto them Moses and Elias(Elijah) talking with him." (Matthew 17:3)

Elder Boyd K. Packer explained:
"One question about Elijah needs to be clear at the outset. The New Testament refers to Elijah by the name Elias. For example, James 5:17, "Elias was a man subject to like passions as we are." The reason we are sure that this refers to Elijah is that Elias is the Greek translation of the Hebrew name Elijah. When they refer to an individual's name, they could not mean anyone but the Elijah of the Old Testament." (Holy Temple, P. 98)

However, the JST translation of Mark 9:1-4 calls John the Baptist the Elias who was there with Moses.

"And there appeared unto them Elias with Moses, or in other words, John the Baptist and Moses; and they were talking with Jesus." (JST Mark 9:3)

Because of this some have speculated that John the Baptist was the Elijah(Elias) who was there with Moses. John the Baptist has of course been called an Elias; the problem is that other scriptures list Elias, John the Baptist, and Elijah as separate individuals (D&C 27: 5-12).

So we can be fairly certain that Elijah was not John the Baptist. The only other way to look at it is if we conclude that John the Baptist was a third person who appeared there along with Elijah and Moses, although he would have been in spirit form only.

To complicate things more, there was a third less known prophet named Elias, who appeared to Joseph Smith and Oliver Cowdery in the Kirtland Temple. President Joseph Fielding Smith explained that this Elias was most likely the prophet Noah. His reasoning goes as follows. Joseph Smith taught that the angel Gabriel is Noah (TPJS. p.158). Luke reveals that it was the angel Gabriel who came to Zacharias to inform him that his wife would have a son. (Luke 1:11, 19, 19). In Doctrine and Covenants 27:6-7 we learn that it was Elias who came to Zacharias to announce the birth of John the Baptist. President Smith therefore concludes that the Elias who appeared to Joseph and Oliver is the prophet Noah. (Answers to Gospel Questions 3: 139)

Others have speculated that this Elias who "committed the dispensation of the gospel of Abraham" onto Joseph and Oliver might have been the prophet Abraham himself.

Bruce R. McConkie stated:
"We have no information, at this time, as to the mortal life or ministry of Elias. Apparently he lived in the days of Abraham, but whether he was Abraham, or Melchizedek, or some other prophet, we do not know. (Mormon Doctrine, p. 220)

As you can see there are different opinions even among Church general authorities.
One thing to consider is that bestowing keys on Peter, James, and John at the mount would have required someone who still had a body. Moses and Elijah were translated beings which physically qualified them to perform their respective ordinances themselves. Anyone else who appeared there would have still been a spirit(eg Elias). So it is possible that if there were any other keys to bestow, it was necessary for Jesus to stand in for the respective prophet. However, there is of course no scriptural record of this.
When it came time for keys to be bestowed on Joseph and Oliver Cowdery, this same third prophet(Elias) could by that time have been a resurrected being, which would make it physically possible for him to perform the ordinance himself.
At the moment there is no other absolutly certain answer to your question that I can find.