I was able to solo this as a 65 paladin. I expected to be killed, but the fight was not nearly as difficult as I expected. I used Infusion of the Faithful to boost my resists to 500 right after the beginning of the fight, and resisted every cast of Disease Cloud. I even resisted it once or twice with only 360ish SvDisease before I remembered to use Infustion of the Faithful. I also used steadfast servant, though I would have been able to win without it.
I used Holyforge, and got lucky with several nice and several more average slays during the fight. I would estimate that the wyvern has 30 to 35 thousand hitpoints, but that is just a very rough approximation. It resisted pretty much all of my procs, and about half of my undead DDs. It also didn't seem to hit as hard as I would have expected of a level 70 mob. I could have easily kept myself healed with just my heal over time and normal healing spells. I did not need to use Lay Hands, Hand of Piety, or potions to heal myself, nor Purification or Radiant Cure to cure myself.
I fought with 2330 AC and 11.5k hps, self buffed, and all have all Combat AAs that are available at 65 purchased. The fight ended with me at 40% health and 65% mana. The fight took about four or five minutes. No enrage.