Here is a good source on cog widths and chainlines. http://www.sheldonbrown.com/chainline/
The EAI cog is almost 2mm wider than the surly. Also, you might want to run the chainwheel on the inside of your spider if that is an option. You can always put a spacer on the drive side of your bottom bracket to get the chainline perfect. I believe this is safer than putting spacers between your hub and cog.