I doubt that .013 and .015 "slop" in your spring bushings/pin is causing your vibration. The type of vibration which comes in at a specific speed is most likely due to a faulty rotating part. Other loose non-rotating components may well amplify the vibration caused by the defective or improperly adjusted rotating parts.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission