Technically a pixel is the smallest unit that a monitor can display. Granted with high dpi monitors, the term pixel has been a bit overloaded but for this jam, that means there can only be 64x64 units of color.
Any trick used to bypass this restriction will probably just look bad and likely negatively affect the authenticity rating.
I’d set your viewport to 64x64, scale it up in whole number multiples to make it easier to see, and accept the restriction.