I think you should be all right on resists. 85% LR is good enough for Ubers, IMO. Although maybe upping your fire resist a bit more via small charms of like 10-11% fire resist would help out. If going with extra Ravenfrost, don't worry about maxing cold resistance, as your cold absorb should take the punch out of any cold attacks. Just worry about fire and lightning.
Chains, Dracs, and Nosferatu's Coil should give you a lot of leech, and after LT fires, you will be very hard to kill when smiting or zealing. The important thing about resists is that they'll help you survive until LT procs.
Thundergod's Vigor gives generous boosts to Vitality and Strength (+20 to both, IIRC), in case you need them, ups your max LR, and has 20 or 25 lightning absorb on it. I have one on my Conviction Zealot, and Gloams heal him in Hell. The healing effect starts to happen when you have about 60 or 70% LR. Once Fade procs, he's pretty hard to kill. But against Ubers, you really won't be facing Gloam-deadly lightning attacks from what I remember. It's usually Meph's poison, painful physical attacks, and icy ball of death that cause some trouble. Thundergod's will add extra hp, though, in case you need it and make lightning worries a thing of the past.
Verdungo's offers +30-40 Vitality (and that adds up to a lot of hp), 10-15% PDR, 10% FHR, and some other minor mods. Basically it'll add even more hp than a Thundergod's will and make you a tougher cookie to crack if someone's beating on you. However, as far as resists go, it's lacking. Useful if you want to stack it with more items granting %PDR, like a nice Vampire Gaze, Stormshield, CoH, or even Fade's 15% PDR, I think, and your resists are good.
Some guys prefer Dungos, Thundergod's, etc. I usually like to test different setups which I think will benefit my builds, then make choices accordingly. I don't really favor one belt over the other. It depends on your needs and what you see as your playing and testing things. If you have more than enough life (1300+ hp) thanks to hefty Vitality, Dungos or Thundergod's may not add much to your build. If you don't, their hp boosts and other mods could be very useful.
Edit: Just saw your post after I wrote this response. It's quite all right to go with Dungos then, now that you have one at your disposal.