I just called my Local NH Dealer - Timmer Imp in Aitkin MN.
Parts man there confirmed what you and others state that the horned plunger (C6NN3N729A) has been replaced by the standard plunger(LA33579B)
I told him the plain plungers would Not work.
He is going to contact NH and see what he can find out.
I sent him the photo below which he will forward to NH.
I guess it's a matter of hoping for the best but not expecting much.