there are two theory on tapered Timken roller axle bearings used in stock 8 3/4 rear ends, the later ones(1965 and on) used the adjusters to set the axle end play from .003 to .010. I have seen Timken tapered roller bearings set up with a light preload, like fronnt wheel bearings either way will work How are your rear axle bearing and end play adjusters holding up now? As already said the axles will break right at the end of the spline that is engaged in the spool or posi, been there done that twice(drivers side is first to go ). Paint the stripes on both axles now, check the left one(drivers side) frequently I have seen a stock axle twist almost two complete spines before shearing(breaking) It does make the car go left when that side(left or drivers side) quits driving