Cam gone flat? Here's a interesting video.

The actual radius on the lifter is not as important as some think...as long as it has a radius [ high point in the centre ]. What it will affect is the speed of rotation of the lifter & long term, possibly how many miles it will do. Doesn't cause a failure during break in.
The original 6 pack cam had the same timing specs as the Magnum cam. The 6 pack lifters were low taper & had a separate part # [ & were used because the 6 pack used stronger v/springs ]. This allowed more contact area at the lobe/lifter interface.