I just killed this guy today for my epic. It was the last piece I needed, so now I've got two level 56 characters with epics.
I used my level 56 ranger for the encounter, because I got enough higher warriors to handle him, so I wound up pulling him (no bard high enough to pull him, only one other ranger there)
When you pull him, pull him to the succor area by the FoB zone. You won't get adds there and it's fairly easy to get people there, makes for a long pull though.
First attempt, we had 18 people, 3 very well balanced groups of 55-60. Pulling him, a moldering ape aggroed on me and bashed me, thereby stunning me and killing me. The other ranger AND the main tank went to pull him (BADDD) and totally surprised our camp. We got him down to 8% health though before our last monk and necro FD'd.
Second try, we had 26 people, 4 very well balanced groups. It was understood what would happen on the pull if I died again, the other ranger would go and drag Sev the rest of the way. Everything went fine on the pull, didn't get hit, then I lagged out for a half a second, got stunned, and wasted like 100 yards or so from camp, just out of everybody's clip plane. Ranger tagged him, brought him the rest of the way, when I was done zoning Sev was at 5% health. I was the only death on the second attempt. Rezzed me, then I went to loot. Here's what he dropped:
Green Dragon Scales (had these defaulted to me)
Dragon Hero Bracer
Dragon Bone Bracer
Spell: Aegis (cle)
Spell: Demi-Lich (nec)
Spell: The Unspoken Word (cle)
Spell: Divine Intervention (cle)
Spell: Disintegrate (wiz)
Be smart about what you cast on the puller. Rune is a MUST, as is the best set of cleric buffs you can throw on the character. Get magic and poison resist up as high as possible as well (Poison was 254, magic 230-ish for me, resisted all but ONE stun, which proved fatal on my second pull). Shamans and necros are a definite must, so are mages for the resist gear they summon.
Sev is easily do-able with 3 good groups 55+, just as long as you're clear on what happens if the puller goes down.