Honestly, I think you should go for Levitate Bronzong over Porygon-Z all together. He would make up for some of your team's lack of special defensive capacity, which really is only being compensated for by Dusknoir. Either that, or ditch Electivire, because more often than not, it's rendered useless by most opponents. (Which really bothers me, because I love the thing. xD) In place of it, you could try a Breloom with any sub-punch or Bulk Up set.
Sorry if this doesn't help at all. ^^; Just figured I'd get it out there.
Bronzong @ Leftovers
EVs: Def 255 / Sp. Def 255