Another wierd question

[turner15]

So I had to replace the bottom edges of my inner sides of the box for my full size fleet. I have the new sheet metal welded in and all is good. However now I have know idea where to drill the holes for the bolts would go? I'm talking about the 1 inch lip, flange thing on the bottom of the inner bedsides.

Any idea how I can get those hole locations? They are square too so I'll need to drill and file to get them square.