Don't know about what mopar may have said in print but most everyone that has actually cc'd a stock uncut magnum head has gotten some in the range of 64cc's. Just like the older open chmaber heads that were supposed to be 68 but almost always were over 70cc or block deck heights always being considerably larger than the nominal advertised dimension.
It's these variations that make it mandatory to measure everything when building a high performance motor and not assume anything.