I gave up on undoing the brackets on the frame and cut the heads off the bolts off with a grinder . I am changing from a 4.3 to a 350 in a 1989 pickup. I had to move the female part of the mount 4.5" ahead but the bracket stays where it was. I welded them on the bench. When the 350 goes in I will line up the holes and weld the bracket to the frame . Good welds for sure.