Just be careful. The drop rate on those Tavnazian Bells is beyond horrible (as you may or may not know already). If you lose the NM fight you WILL! have to get another bell. Make sure your group can take it when you go. It's best to have 2 tanks if you don't have a lot of DD because the NM likes to use AoE (get rid of shadows) and then immediately do Dimensional Death before you can get shadows back up.

If you were taking people from your level range alone, I'd suggest 6 people at the very least. I know that I can barely squeak by with 2 healers though it's still a mess (I lost someone's bell once). Usually with just one more level 75 DD it's much easier. A 75 NIN built to DD can probably take it out fast enough that one WHM might not run out of MP healing him.

GL ^^