Boy, that datasheet brings back memories, back when the IC mask was actually (for some reason) included.
Those early CMOS parts had a tendency to burn up if the inputs of unused sections were left floating. If the logic included inversion you could get positive feedback from the toggling output back to the floating input, and the frequency, and corresponding power supply current, would race way beyond the parts spec.
Is this a hobby project?
Edit --> I just noticed that Berkeman discussed this on a different thread from same OP.