I inherited a Hawthorne Village set that includes Spectrum F7A & B Units.  The E-Z Mate couplers on the B Unit are enough lower than the F7A & full dome passenger cars that they frequently uncouple during operation.  I replaced the couplers with style number 78005 center shake couplers which match the one on the rear of the F7A, but this didn't fix anything.  How can I raise the coupler height to match the rest of the train?