I have 300 feet of 1/2 inch anchor line and 6 feet of chain which pretty much fills up the anchor line box. Please note: This is with the anchor stored out on the bow pulpit and the anchor line running back into the box , if you are storing the anchor in the anchor line box not sure you would get all 300 feet in there.
What model did you order, vertical or horizontal. The horizontal might but you a bit more space for line.
The issue is not how much line the locker can store but rather how much line can the set up handle without jamming. As the line piles up the distance from the pile to the capstan gets shorter and at some point the stiffness of the line causes it to stop laying down and that will cause jams. If using a new soft line you will be able to handle more length.
Have not ordered the windlass yet as I am still trying to figure out best solution and configuration. Right now I have no windlass, just hand coiling the line as I feed it into the locker. Am going to look at the Lewmar