I believe I over exposed one layer and under exposed the next, painting out on a mask where I wanted the most contrast change. One thing to note is you can accomplish a lot of this conversion in the color version by working in the B&W adjustment mode, pushing and pulling the color sliders to suit. Flatten the original then take it into SEP, if needed. If you go to SEP, use it as a layer and mask again, keeping what areas you want more or less contrasty and again, painting out that which you don't like.