What do you mean by using a half link chain?

On industrial applications, you can find what is called a "Half Link", which only uses 1 valley of a sprocket instead of 2 valleys like a normal full link uses. It's for fine tuning chain length if you run out of adjustment using normal methods to take up the slack. I'm not 100% certain that they are available for 520 chain though. Most hardware stores, industrial supply stores, and home/farm/ranch stores should have these in inventory.