You lost a lot when you made this monotone. Quadtone probably wasn't necessary. I think a straight desat, with or without a tone, would have accomplished the same effect.
That said, I think it needs more contrast and some strategic dodge and burn to make it work. It strikes me as kid of flat. The color version has a nice sense of depth and space that is lost here. I think a more careful conversion is needed to bring some of that back.
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