MCI 8 question on engine blower motor

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On my mci 8, Up on the blower motor in between the squirell cage there is a plate that the motor attaches to and on each side of that is a small plate. My question is can those be shimmed out for a tighter fit. That plate shakes back and forth. There is probably at least 1/8th to 1/4 inch gap on each side which is giving it 1/2" play. I have replaced all the bushings with poly bushings it it still shakes back and forth.