I thought it was clipped on the driver's side of the brake/clutch pedal pivot bracket from '63 to '66. Going from memory sadly, was unable to confirm on vehicle.
You're absolutely right. My ash tray housing was still there and had the clip in it as well as the telltale square hole instead of round. Did not have a '66 FSM to refer to. Did not mean to intentionally mislead.
Just something I noticed. 65 and earlier darts look rounded. The 66 looks like a cross between a 65 and a 67.
My bet is that a lot of 66 related parts are VERY similar to 67. As others have said the turn signal is on the right side of the ashtray, just like in 67 up