I agree with the fellas about modern boxes... yuck.
I don’t have a big bolt, mine is a 1 ton, but this is what I did with my duals.
https://photos.app.goo.gl/CmcwJq9eMsjBnoQQAI have a build thread on this in the Tons of Fun forum but it is buried a few pages in by now. It might give you ideas what a stock box can look like. Also search up Plowboy. He has a big bolt that he built a bed for except he widened his tailgate, front panel and built tubs in the box. His is a sweet truck and he uses it to work.