That causes a problem because the rear O2 bung on speed daddys is in the tail peice with the flange that you are talking about eliminating. If you slip fit some peices of pipe you will have to weld in a new O2 bung. If the rear flange is saveable I would drill it and reuse it to save you from having to do any welding. If you have to get somebody to weld for you it is just your preference on the way you do it.