Bed cross sill not lining up with frame pad 1966 C10 SW

[Steveoreno]

Now this is an odd one.....thought I would go ahead and mount my bed cross sills just to get them out of the paint bay so I could start paint work on the box sides, wheel houses, etc. When I went to mount the intermediate sill (the second one back from the cab) the holes would not line up...not even close. Thinking that perhaps one of the sills in the kit must have different hole spacing I checked all three and they are identical. The bed sill holes are 35 1/2" and 31 1/2" apart on all three while the holes in the frame pad are 37 1/2" center to center. So the solution apparently is to drill new holes in the intermediate sill to fit the frame pads....this would leave me wondering whether or not the holes would then be out of alignment if I ordered pre-drilled bed wood...or should I just assume that they would not line up and order non-drilled bed wood. My biggest question is why this is so....should one of the reproduction sills have been drilled different than the other two....is my truck an anomaly.....what the heck? The width of my frame on my 66 C10 short wide is 30 1/4" inside to inside at the center point of the intermediate mounting pad location. The picture shows the silver marker where the frame perch holes fall on the sill when it is lined up. Any ideas?