[chevyrestoguy]

It's interesting reading, but I think that it doesn't address or take into account that other things are attached to the frame in that area. Things like frame crossmembers, bed crossmembers, bumpers, etc. Each one of these items strengthens the entire assembly and takes up a degree of total stress. I also have to question the data that stated that the weld-in and bolt-in notches are 80% weaker than stock, when you have added .250" steel plate on the outside and underneath of the existing framerail. You have also added a .250 thick triangulated area at the notch. My '64 is originally a C-20, and my frame was double reinforced by the factory in this area before the notch was even added. I used the CPP bolt-in notch (.250 thick) and fully welded the perimeter. If you take into account the thickness of the original frame (.1875), plus the reinforcement (.1875), plus the thickness of the notch assembly (.250), you have a thickness of .625. (5/8ths of an inch). That's plenty strong, and that's not including the perimeter welding.

I could see the data being a concern if you have a leaf spring suspension, because the leverage between the ends of the spring is putting a strain on the frame at the center point between the two. On a coil spring suspension, the strain is at the forward attach point of the trailing arms and at the upper coil spring attach point, which are both forward of the c-notch.

I'm not coming down on the thread concerning frame strength, quite the opposite. I think it's a great thread with very interesting information that the OP put a lot of time and effort into. I'm just adding a little bit more insight and hoping to add a little more food for thought.