On my '68 4500 the shifter used to be sloppy as heck. The operating lever, where it goes into the transmission housing, is secured with a bolt that fits in a slot on the shaft that goes into the bell housing. The slot had worn badly. I took off the lever and cut a slot through it perpendicular to the bolt and in the middle of where the bolt passes through. Now when the bolt is tightened it clamps the lever tight on the shaft. The difference was day and night. Nice crisp shifting.