Toolbox length

Hey guys and galls. Sorry to ask but I'm away from my truck for the next couple months and don't want to just measure a random stranger's bed. I'm looking at buying a crossover toolbox and have googled and searched TW to find a definitive answer and haven't come up with anything.
What is the max length for a crossover so it doesn't sit over the sides of the bed? I'm looking at this weatherguard: https://www.weatherguard.com/truck_tool_boxes/view_products.php?subcat_id=9 , and the top is 66". I found someone that said they had it in their truck but (attempting to envision in my head), I'd think 66" is too wide. If the bed is 57.5 that would mean the sides of the bed would have to be at least 5 inches each for this box to fit. In my head they don't seem like they are. I'm picturing 3"-4". Is anyone up to throwing down a measuring tape real quick for me?