I have purchased the watch but not picked it up. There is a thread on watchuseek.com about this watch. It certainly isn't correct as far as parts match and date codes are concerned. The first USA Chapter Ring was dated 1964ish so that is most likely a replacement caseback and if it was an M3, the pillar plate & component coil assy would be different. Pre-1968 Pillar plates would have been Zinc colored and not Gold so this pillar plate is a 1968+ replacement. And if this were a 1963 Chapter Ring watch the coil assy would have been a capacitor facing up 3 wire assy. This one is a 1965+ 2 wire assy. Possibly correct 2 wire for this watch dating 1964/65+ but the caseback date code does not match anything normal for this Chapter Ring. Chapter Ring Case 2531 (Gold Filled was the first USA Chapter Ring Spaceview in 1964) and Chapter Ring Case 2528 would have been around 1965/66 and would have been SS. There was a A2528 case also.
It's a real Chapter Ring watch but it has some mismatched parts on it and needs some TLC.
Another poster wonders if that is an M8, not an M3, which would be awesome. I'm really looking forward to picking this up!