I unbolted the front spring hanger . Cut it and shaped it to fit inside the frame rail . Cut the frame just enough to install and weld it up.
Rear I drilled a hole and welded a sleeve.
All I can say is measure twice and cut once. Ha ha, Whole job took me about 30 hrs. to complete. But that's also changing over the 3rd member , backing plates ,brakes and drums. Not to mention, New axle seals, long studs, Etc. etc. etc.