This has come up in other threads more recent than 1998; the search engine will find them. There seems to be no connection at all with The Dream of Olwen, and nobody was ever able to identify a Dream of Alwyn so far as I remember; I think that Barry may have got the wrong end of the stick somewhere.

We may be looking at a red herring on the lines of the mythical "broadside original" of Fields of Athenry, which also seems never actually to have existed. At all events, it's been gone into in more detail elsewhere well after this old thread was forgotten.