The best way to get the contrast increase you need for quality pt/pd prints is to bleach and redevelop the negative in either a staining developer like pyro or pyrocat, or alternatively, redevelop in a fresh thiocarbamide sepia redeveloper. Either of these solutions will add actinic density to the highlight areas of your negative and give you a contrast boost. Mostly likely the cause of your graininess is the amount of contrast agent you had to add to the print sensitizer solution to print on such a flat negative.