3.7 * 16 = 59.2V
So 60V would be more correct, not 64V. It is based on the "nominal" voltage, not the max voltage.
Bottom voltage of 3.2V/cell would be 51.2V
3.2 * 16 = 51.2V
3.7 * 16 = 59.2V
4.2 * 16 = 67.2V
So your working voltage range is 51.2V - 67.2V. However, charging to 4.2V will not do your cells any favors and will actually keep your cycle life down in the 100's of cycles. Just changing to 4.1V, or 65.6V, for your top end will give you close to 1000 cycles. And then dropping to 4.0V, or 64V, will give you over 1000 cycles.
Looking for a charger that can do 64V is a lot easier than finding one that can do 67V.