>Which makes some sense; until at least Pope Urban, the Catholic Church was happy to perform both mixed sex and same sex marriages

That's not what your [3] says.

>Nevertheless, Historian John Boswell argued that Adelphopoiesis, or brother-making, represented an early form of religious same-sex marriage in the Orthodox church.

>Alan Bray saw the rite of Ordo ad fratres faciendum ("Order for the making of brothers") as serving the same purpose in the medieval Roman Catholic Church.

John Boswell died of AIDS. No mention of how Alan Bray died, but he was also homosexual. Hardly impartial sources.