Are they to long to fit, period or are you just observing that they are longer?
Another thing to realize is that overall length does not necessarily correspond to effective length. You can have two pushrods with the same effective length but a slightly different overall length but both should work just as well. Effective length is the distance from the tip of the ball, to the bottom of the cup and cannot be measured with typical hand tools.
Putting a shim under the stands will require a pushrod that is longer by more than the thickness of the shim. The reason is that the valve stays in the same position, so the rocker also has to rotate toward the valve on the shaft, moving the adjuster screw even farther away from the pushrod.
Lawrenceville, GA