You shouldn't have too much trouble. I beat him with Vivi, Quina, Garnet, and Zidane in my party.

Zidane was level 68 and did about 7000 with thievery.
Garnet was level 72 (everybody else had virus inflicted on them, so she gained about 20 levels by the time I reached Kuja).
Quina was level 51.
Vivi was level 60 and did about 4000 with blizzaga, when necron had shell cast on him.

All of them had auto haste, auto regen, and auto reflect equiped.
Garnet and Zidane also had auto life equiped.

I never attacked with garnet and really didn't use her for much now that I think about it. I figured I would use Quina's Angel's Snack ability to remove the status changes inflicted, but that didn't really happen either. I would cast Blizzaga on my party and reflect it back to Necron for about 4000, and I would use Zidanes thievery for about 7000. Thats about all... now it's time to start my new game.