As I suspected, it's #004. It used to reside in or near Portland, Oregon for many years. I first encountered it at the meet-and-greet before the Monte Shelton Classic in 2011, where I participated in the green Alfa Spider in my profile pic. #004 crossed my path a few more times at concours and vintage events in northwest Oregon. I'd heard that it had been sold, but not where.
Some time later I was visiting my mom after she moved into assisted living. We were going through a box of old photos, mostly of us kids but a few from car events she had attended (apples and trees, as the saying goes). At one point I saw a 166 similar to this but with a slightly different air intake, taken at Pebble Beach in the 1980s. Mom hadn't noted the specifics of the car but I suspect it was #002, owned for a long time by James Glickenhaus.
The traditional reasoning behind #004 being the oldest original Ferrari versus #002, with its lower serial number, is that #002 had been in a serious crash early in its career, and many major vomponents had been sourced from other cars. #004 has more of its original equipment (I'm faintly recalling that the rear axle assembly and part of the chassis had to be re-sourced for #002, and I'd love to hear from someone who knows more).
Still, hard to realize that there's so little distance in time between the cycle-fendered, torpedo-bodied look of #004 and this envelope-bodied 166 MM Barchetta, driven at the FCA's 2023 Annual Experience by keynote speaker Derek Bell. Here he is preparing for a demonstrationlap around Oregon Raceway Park.