The outtakes
There is a generous helping of outtakes on the DVD. Two in particular show that the movie could have been very different.
One shows the violent incident where Harry earns Ken's indebtedness and loyalty. As it stands, with a different actor playing the younger Harry, it is too abrupt a change of style, as if part of a different and Tarantinoesque film had been spliced in. I think it was right to edit it out as it would have needed further accompanying scenes to meld it into the story.
The second is even more revealing. It concerns the seduction (abduction?) of a young boy by a paedophile and has no connection with the existing plot. I imagine there was originally some thought of including a further major plot-line (possibly with Ray redeeming himself by rescuing the boy?). This would have made for a wholly different movie and it would have been a tricky theme to have handled sensitively. It might have unbalanced what ended up as a very fine movie, but I should not be surprised if Martin McDonagh returns to that theme in some future film. Plenty of material for it in Ireland.