FYI we did this at 58 (PLD, SAM, DRK, WHM, BLM, RDM) with no real issue. SAM helps a lot with 2-hour and intimidation. Ootherwise, just be aware of how the Shadow Lord works (ie don't cast magic on him until the DDs are hitting for 0; WHM spams Curaga and Benes at their discretion during the second form; save WS (Icarus Wings are nice) for the second form (make sure the PLD is fully healed and then uses Spirits Within); offensive mages can unload on the second form; RDM can fairly safely Convert at the top of the stairs behind the SL).
Bring meds.
As far as getting to the top goes: Sneak and Invis till you get the the mini rooms with the gobs. Then just fight your way through (all EP). Sneak again through the Quads and Eyes. At the teleports, Invis and hope there are no demons at the other side of each tele (you automatically lose Invis on teleportation). They are only DC so you can handle them at 58+, even with a link.
Oh and one really really really important note: MAKE SURE EVERYONE IN YOUR PARTY SPEAKS WITH PRINCE TRION!!!!!!!!!!!!! (there is nothing so wonderful as spending 1.5 hours getting to the top only to hear the words "Um... It won't let me in")
Have fun :)