Clasico will be tough whoever plays. Sure, Mascherano isn't as good technically as Busquets but he is no slouch technically and he is a lot more mobile than Busquets which will be an advantage.
Playing with Mascherano as DM essentially gives us two CMs and three CBs. Not very appealing at all.
We're lucky Madrid is in such shit form going into it. This is one of the few times I think scoring on them early would actually be a major boost to our chances of winning.