This is the approach I took. Low tech but quick and easy. I used grade 8 5/16" bolts for the pivot pins. First step was to drill down the middle of the bolt through the hex head to a depth of 1¼" followed by a lateral hole in the side, where the middle of the hinge arm locates. Then cut a spiral groove above and below the lateral hole. 45 degree grease nipple fixed to the bolt head
This is what it looks like in place
I tack welded 1" squares of 1/8" steel top and bottom of the box to add some meat to the pivot pin mount, then added a stop that sits snugly against the side of the hex head to keep it from rotating. The nyloc nut allows you some greater leeway to adjust the tension on the hinge arm pivot.