The original Dana posi units (both 8 4/4 and Dana 60) thrust buttons are two piece with a very soft connector that goes in the hole in the center of them and is suppose to be peened over to keep them in place. Do you have the thrust buttons now? If not you will have to get them and install them before being able to set the axle end play, that or switch to non adjsustable the Green axle bearings Make sure and use two gaskests, one on each side of the backing plate to the axles, you might want to replace the inner axle seals in the axle tubes also now that the car was leaking grease out of them Ain't fixing old cars fun