Online sites with other well known early christian scriptures are at Early Christian Writings (though the dates they provide are ridiculously early, probably to cut down on hate mail from Bible literalists) and comparative-religion.com.

Incidentally, to say that the authorship attributions of the apocryphal New Testament books are downright silly is only to say that they are slightly less plausible than the attributions traditionally given to the canonical texts. And if you begin to read through very many of of the apocryphal texts, you’ll notice that there are so very many divergent views about who Christ was and how he fit into the puzzle that there’s something in them for every religion to cherish as evidence that their church practices the original, true Christianity.

Moses and Elias at the Transfiguration
Question: “What was the purpose of the mission of Moses and Elias at the transfiguration of the Savior, when he took Peter, James, and John with him upon the mountain?”

Answer: It is very apparent that this was a sacred mission which in all of its particulars was not revealed to the world. The only mention of the purpose of that visitation is given by Luke to the effect that Moses and Elias spoke to Jesus in relation to his death which should be accomplished at Jerusalem. The questions put to Jesus by the apostles as they descended from the mountain infer that there was something said in relation to the restoration of all things before the second coming of the Lord. However, they were placed under a strict command not to reveal what had taken place, even to their associates, until after the Savior’s resurrection. It is quite evident that much that took place was of such a sacred nature that it was not to be revealed to the world.

PETER’S TESTIMONY
Peter in later years bore witness to the significance of this heavenly vision as a testimony of the divinity of Jesus Christ, in the following words:

For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty.

For he received from God the Father honor and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased.

And this voice which came from heaven we heard, when we were with him in the holy mount.

We have also a more sure word of prophecy; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts:

Knowing this first, that no prophecy of the scripture is of any private interpretation.

For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost. (2 Peter 1:16-21.)

It seems apparent that while on the mount these three apostles received an endowment and a commission to act as a presidency in the Church after the crucifixion of our Lord. The Lord revealed to the Prophet Joseph Smith the following in relation to this spiritual manifestation:

[He then gives the WOJS quote from above]

12 And there were gathered together in one place an innumerable company of the spirits of the just, who had been faithful in the testimony of Jesus while they lived in mortality;

13 And who had offered sacrifice in the similitude of the great sacrifice of the Son of God, and had suffered tribulation in their Redeemer’s name.

14 All these had departed the mortal life, firm in the hope of a glorious resurrection, through the grace of God the Father and his Only Begotten Son, Jesus Christ.

Then later:

36 Thus was it made known that our Redeemer spent his time during his sojourn in the world of spirits, instructing and preparing the faithful spirits of the prophets who had testified of him in the flesh;

37 That they might carry the message of redemption unto all the dead, unto whom he could not go personally, because of their rebellion and transgression, that they through the ministration of his servants might also hear his words.

38 Among the great and mighty ones who were assembled in this vast congregation of the righteous were…

He then goes on to list all the great prophets including Moses and Elias.

This only becomes a question if you assume resurrected or translated bodies cannot visit the spirit world. I don’t know of anything to back that assumption. In fact we know spirits can visit us embodied folks here. Plus the Father had a body during all of our intereactions with him in the pre-mortal realms. So if this is the case what is the issue with and embodied Moses preaching in the spirit world?