I'm building a new box assy. and having a little trouble w/placement of the two middle cross sills ! I find they line up with the holes in the metal strips at 23 1/8" and 50" from the front panel. Although they would not be bolted through the angle strips, as they don't line up . Am I on the right track ? My cross sills have no holes drilled in them so it makes it a little harder to figure out . Thanks for any help ,Mark