Actually the resistance of the oil pump, tends to pull the cam to the rear of the engine, as does the taper on the lobes. I personally do not see the need for a cam stop on a slant six, unless using roller lifters. I used a cam stop on one of my engines (just to try). Set it with .007 clearance to the cam. After a season of racing, removed the timing cover, and saw no sign of the cam bolt contacting the stop.
