Take a pencil and a popsicle stick. Take your 1964 quarter and another silver (pre 1964) quarter and place the popsicle stick on the pencil (pencil is lying down on the table). Put one quarter on each end of the popsicle stick and balance like a miniature seesaw. Mark where the two quarters rest on the stick. Remove the second silver quarter, replace with a clad quarter, the 1964 side should go down.
If you don't have a second silver quarter, do the same, but start with two clad quarters, make them balance, mark positions, then replace one with your 1964 quarter. It should make that end of the seesaw go down.