Your notation, 1 Enoch 96:2 refers to the righteous rising into the cleft of the rock, is particularly interesting to me in light of Thayer's discrimination between the Greek words petra and petros.
1 Enoch 95:2 In the day of the sufferings of sinners your offspring shall be elevated, and lifted up like eagles. Your nest shall be more exalted than that of the avest; you shall ascend, and enter into the cavities of the earth, and into the clefts of the rocks for ever, like conies, from the sight of the ungodly;
Having said that, I do not believe that the quote from Isaiah refers to Abraham as "rock," rather, I believe that it refers to God as being that Rock:
Isa 51:1 "Hearken to me, you who pursue deliverance, you who seek the LORD; look to the rock from which you were hewn, and to the quarry from which you were digged. Isa 51:2 Look to Abraham your father and to Sarah who bore you; for when he was but one I called him, and I blessed him and made him many. Isa 51:3 For the LORD will comfort Zion; he will comfort all her waste places, and will make her wilderness like Eden, her desert like the garden of the LORD; joy and gladness will be found in her, thanksgiving and the voice of song. Isa 51:4 "Listen to me, my people, and give ear to me, my nation; for a law will go forth from me, and my justice for a light to the peoples.
It's pretty clear that this section is a call for His people to return to Him and cast their gaze upon Him.
Having said that, it DOES appear that there is an allusion to Abraham being hewn out of the Rock; but it is but an allusion, not an actual renaming of Abraham.
And in that respect your interpretation of Isa 51 parallels the non-Catholic Christian interpretation of Matthew 16 - i.e. that Peter is the first to be hewn from God (The Rock) having been the first to receive the revelation from the Father that Jesus Christ is Lord.