Ok, since this is another topic about this quest I made a quick video showing how to do this.
(video was made on local server by using gm powers to teleport, otherwise it would took too long and I would probably not do this ;p)
My bet is that in this and all previous cases player didn't talk with enough number of ghouls and went to talk with Wally after first time he saw his name in dialog. It doesn't matter in which location in Necropolis you talk with them.
Note: not all ghouls got quest dialog, sometimes they will just "argh!" on you but it does not chance quest status (talk counter).
You can buy this base alone, without gang (you will have to create one like I did in video) or as gang leader buy it as next base. All you have to do is to have 350k in inventory to be able to buy it.
SPOILER ALERT FOR THOSE WHO WANT TO MAKE THIS QUEST ON THEIR OWN!!
http://youtu.be/hCNjjVxmeQg