I am going on gut. I have seen a lot of c. 321 Seamasters, but have never seen the watch with that dial. Now, the price alone would make me pass, and there are plenty of no questions pieces floating around with the silver dial (and I understand the potential interest for having a purportedly rarer piece), so I wouldn't roll the dice if you are worried about the $3k without a lot more input and comfort. I do agree with the comment that it would be an odd piece to fake, but at $3k there is a potential explanation. I have let pieces go in the past due to uncertainty, as sometimes the adage better safe than sorry seems to apply.
And is that the only pic? No movement, caseback, crown side pix?