I think then, 2 reads on an Analog input every 8.3ms will cancel out the 60Hz portion. (i.e. average of)
I'd not agree, you would get just opposite results, beating two frequencies may produce slowly changing bias in the data pull. To minimize an influence of the mains, you better to sample as much as you can with NON-multiple to 60 Hz sampling frequency. Averaging interference, statistics math decreases a noise proportionally to sqrt(Nsamples). For example, taking 100 samples you are reducing interference by factor 10 times, or 20 dB.