Cam movement

Does anybody know what keeps the cam in the 460 from moving? Does the cam bolt keep the cam from moving backwards or does the bearing in the back of the block keep the cam from moving towards the back of the motor? I have excessive movement in my cam. The cam bolt backed out which allowed the cam to shift towards the back of the block.

The cam retainer plate...if the bolt is tight.

The cam should not touch the rear plug.

Thanks. That's what I thought just wanted to confirm. Thanks again.