Max lift on stock guides and seals?

The older books always said .520 was it. That fit the "509" usage and like others said - between rocker issues and pushrod angles - you will lose at least .020" from that.
Hughes tends to match thier tech with thier parts as opposed to "Mopars in general". If they used a heavier spring - as in thicker wire or something - they may not get away with as much total lift because of the coil interference. The ramp speed of thier camshafts that have that shorter total lift may require heavier springs and thus require guide work. They also may recommend cutting the guides to run the positive seals rather then because of a lift interference issue.