To keep from having to order a new elbow to the exact measurments simply cut the 4 corners of the elbow down a good 1". and make a new 1" bend on the lips. right now you have a 1/2 " lip witch will not cover the little over sized filter hole. flatten out the 1/2 lip and make it larger so to be able to screw into the lips and cover the hole. seal gapsand seams with metal tape or chaulking.use short screws so not to get into the way of filter.