i have no doubt in your hearing, you can tell the difference in ticking between a 861 and 321. The large second hand is also clue, they run different when you compare them. I'd say the 861 runs smoother.
I wasn't sure if the transistionals had the same Chrono hand as the 321's.. Are the 321's longer and more pointed?
I'm game to play along (god that's a beauty by the way).... I'm going with 145-012-67, serial 2654xxx