670zx is the 3 head with tape monitor version of the 660zx which while still 3 head, has no monitor while recording, both with analog meters. I have 2 660zx, with one for sale, just awesome Dolby B only decks. The way Nak cleverly displayed the output on the meters during calibration with the internal cal tones was neat. Of course, today it's hard to see why they ever offered decks with 3 discrete heads, and no monitor, but it made sense back then. I also have 3 680zx, which was basically the next version of the 670zx with new flourescent meters, and minor updates. One of the 680zx is for sale. They are just classic decks from the heyday of that period. ALways have a lush sound, very full. Their biggest issue today is orange cap disease, especially with the 680zx, which all seem to have it. I have recapped mine. Normally only the 4700pFs in the oscillator circuits succumb on the other decks of that era.
It is very common for the older Naks with black anodized faceplates to have a purplish cast in the right right (wrong?) light, especially as a camera captures it with flash. It can normally be seen with the naked eye in direct sunlight, but in normal room incandescent lighting they remain black. The rack handles are painted, not anodized, so they stay black, and the bezels are plastic, so also stay black.