You can make them out of plywood - usually 1/2" - have done it many time but not on Sears. Where the insert sits there are usually four flat tabs coming out from the casting that the insert rests on. On your insert take four small #6 flat head wood or self tappers and screw them into insert at same location as tabs. this allows to adjust the height. Trick is to make the insert as snug as possible. Goodluck