Allegorical reading of the bible was and is widespread, not only by Christians, but also by Jews (https://medium.com/rambles-through-history-and-philosophy/the-gift-from-alexandria-c3e976e4cea9).

Regarding 'alternative' texts - there are many of them around, and usually they are not very interesting (read any book about Gnostic beliefs); looks like the ancient Christians did a good job collecting the 'best' documents (the same goes for the Jews that chose the texts for the Old Testament).

We know that there were many different lines of Christians (e.g. Marcionites, or Gnostic Sects close to Christianity). While the interpretations may be interesting (Origen for example suggested that in the end all souls, including the devil, will be redeemed) but I don't see any indication of texts that can rival the texts included in the New Testament. (Origen counts as a Church Father - this is a different category of texts.)