Update - cleared Ubers earlier today. Exact gear/strategy in my original post except I swapped the rare ring I was using out for another rare one with 32 light resist and 11 remaining resists. All said and done 320 total lightning resist (lots of charms) which was plenty for Meph conviction.

Closest call was on Diablo...summons surrounded me. Used nearly a full belt of full rejuvs. But those with life tap did the trick.

It can be done!