Pix would help.
Can't speak to your 260, but on my 330, the microwave reats on a couple of 1/2"x2" strips (one front and one back) that run parallel to the front of the unit. The rubber mounts are removed. The strips are glued to a 1/2" sheet of plywood about the size of the microwave. The whole thing rests in the cabinet. The microwave is secured by screws in each corner that extend through the cabines base, the plywood, the 1/2"x2" strips and into the recepticles for the rubber legs. There are a couple of screws in the center of the unit for good measure.
