From your post I am guessing that the stud is stuck in the block? I used vice/multigrips to get a good grip on the end of the stud to loosen mine but I found it was important to hold (support) the pump and bracket as you are turning the stud. The weight of the pump causes it to bind in the block making it difficult to turn otherwise. Also, have you tried sliding the pump foreword on the stud so you can apply penetrating oil at the block opening. Failing that, have you tried removing the front support bracket to get access to more of the thread to work with.
Good luck as its a bummer to have to remove the Fan shroud.
Brad