when we fabricated frames for our race cars since we had no cad program we would build a jig and laid out all the important control points with jig attachments using laser, plumb bobs and other measuring tools. If you don't have the equipment to read the frame you have are you not setting the frame on a jig to fabricate fixtures to pick up the control points so that a modified frame can be fabricated on that jig? I'm confused how you are going about this, pictures look god but give no help to measure out a frame. The diagram I posted of the frame gives all the measurements to fabricate a jig to build a modified frame.