A thrust plate bolts to the front of the block and controls fore and aft cam movement behind the timing chain assembly. The cam retaining bolt and washer are indexed to fit over the keyway of the cam. Note the relationship of the dots on the crank and cam timing gears. While some engine builders recommend degreeing the cam, Bill Jenks mentioned that since the cam was reground on a machine that registered everything off the keyway, there's no chance of the lobes being off time. Fifty years experience can't be wrong.