I've found Daetwyler's 412 #36. The picture reproduced here was in Moore's 1st edition without precision of the location, yet indicated as coming from Alfa Romeo's archives: hence it is to be seen quite often. Moore wrote an article on 412s in Thoroughbred and Classic Cars november 1981 where another pic with #36 appears, wrongly captioned as "Bremgarten postwar". But the background with white/red curbs should have helped, and eventually in A. Cimarosti's book "Grand Prix Suisse", there is one further pic with #36 and others of the racing course and painted curbs.
It is the "Prix de l'ACS" (Automobile Club de Suisse), Geneva (as from the detail here above), July 30th 1950, race won by Daetwyler, 26 laps in 52'59"1 at 117,769km/h, with a 3 laps (!) gap over the second, Albert Scherrer in a Jaguar XK120. The 412 ran there with blowers.
As for Simon's opinion on the number of 412s built, Stu, I know your obsession, and I had preventively already answered you here