Wirefeeder, assuming you are sectioning this frame in a more or less straight and flat area.....I would cut it at approximately 30 deg and install a sleeve at least the same thickness material . The length would be twice the height of the frame rail involved as long as you have clearance to fit . Rosette weld/spot weld minimum four spots per side of each rail plus leave about 1/8 gap between rails with a bevel on rails to make full penetration with sleeve when fully welded together. This method has been done in our shop successfully. Also if its a late model vehicle you might have to check with your DOT about VIN numbers etc. If its an older vehicle Weld On
Hope this helps Jim uhohjim1@aol.com