I played with contrast masking and shadow/highlight, then used the channel mixer to convert to monochrome. I then tweaked it a little using curves. Finally, I used the Gradient Map to convert it to a quad tone (dark green, light green, medium blue and very light blue). After applying the gradient map, I reduced the opacity of the map to about 30%. I then used unsharp mask, and touche dup the curves for the midtones.