k-frame holes dont line up

Several ways to do it. It all depends on how accurate you need it. I would consider drilling two 1/2" holes through each frame rail in the same spot, horizontally. Then I would get some 1/2" all-thread and some 2x3x1/4" plates with 1/2" holes. You may want to double up on the all-thread and the holes. Snug the nuts up to the frame and mount the k-member using the holes that fit. Bring the frame rails in the the all-thread until the holes line up. You may want to take it a little farther so that when they spring back they will line up. Go slow and watch out the the all-thread is not stretching. An alternative to the all-thread would be some grade-8 bolts welded or otherwise attached to a bar between the frame rails.