mine were probably around 2 inches apart but you dont have to be real precise, just make sure your spaces are equal so everything wears evenly and it looks nice haha.
this is a pic of my box its not the best picture but its all i have right now. you can kind of see the spacing and what yours will look like
I have 2 of these boxes now just like the same setup your going to make... if you want i can take some pics for you tomorrow once its light out just let me know.....
woops hopefully that works if not just click the link