On gundrak on the troll side theres a nice BoE neck that drops that has a nice bit of def that i used until i had enough badges. The first boss in HoL has some nice shoulders and even Colossus drops some def shoulders with a socket that im still wearing. Theres a quest in zul'drak that gets you a nice tanking mace http://thottbot.com/q12857
Theres a ton of BoE blues you can get from the AH (if there any up) that will get you to 535 with enchants and if you have it id go ahead and spend the gold for the titansteel shield.

As far as doing some of the bosses i have a video here My heroic boss compilation video that i made while i was still gearing up and i was in mostly blues and some greens too.

A tip for gundrak on the Colossus boss is to drop 3 healing stream and 1 NR totem. That alone will heal you through the pools that the elemental spits out. Then just tank and spank. On the first boss on the tank side i just drop 2 fire (4 if you need) to pick up the adds and just burn down the boss. and like Hachoo said park your dps up the stairs and the poison nova wont hit them. as for trash on that side i find that poison cleansing totem really helps when they spit. Hope this helps and good luck