you cant really squeeze him in there without losing 11 goblins, or down grading all your heroes. Either way, you losing far too much for little gain (do you really need that much firepower at 500pts? its not like you will be versing aragon
). You could upgrade to the spider queen. She has less fight and str, but hers is high enough, and the extra attack, broodlings and 2 extra might (the broodlings and might make her sooooo good) make her more dangerous overall (she can chew through troops at a staggering rate). Thinking about it, Im strongly considering changing to her, as there will be less magic and archery to shut her down. The spider queen is MUCH softer, but there is far less to hurt her.
I would also like to see some experiments with Dwellers in the Dark, the high fight and movement make them quite nice, although if I knew i was going to vs a D6 army I would never consider taking one. I wonder though. If i was going to vs an army such as rohan, I would consider taking one. Despite rohans TWs, its fast movement neutralises that; add to it that rohan gets no spears, and they dont have the burst damage to kill it (they would wear it down, something which wouldnt work). Plus no spears means its easy to attack just 1 model and regain a wound
ps, if you want to use druzhag, try taking 2 bats instead, its cheaper and can get to almost any location (they are like mini dragons with druzhag) (probably best if your taking some wargs or something as well so your making the best of Druzhags high price). I havnt tried it myself, but I know how great bats + druzhag can be)
pps, Groblog, 2 shamans and a captain (with full gobs) has become the core of almost all my armies now. Durburz isnt needed because we have fury everywhere