I'm trying to do the finite element analysis on whether two or three blades would be better. Oh and by the way... Don't try this at home kids...! But I seem to recall someone might have tried the two blade scenario already?
It has been tried with varying success, but I don't believe anyone stuck with it as it didn't really do much. I would bet that, as far as lift goes, the best bet might be just to stick with the HL blade on its own. Won't help with mulching though.